JP4517949B2 - Nickel oxide powder for electrode of solid oxide fuel cell and method for producing the same - Google Patents
Nickel oxide powder for electrode of solid oxide fuel cell and method for producing the same Download PDFInfo
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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
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Description
本発明は、固体電解質型燃料電池の燃料電極などに使用される酸化ニッケル粉及びその製造方法に関するものである。 The present invention relates to nickel oxide powder used for a fuel electrode of a solid oxide fuel cell and a method for producing the same.
一般に固体電解質型燃料電池は、多孔性のＬａＭｎＯ３などからなる空気電極、緻密な安定化ＺｒＯ２などの酸素イオン伝導能を有する固体電解質、ＮｉＯ−ＺｒＯ２などからなる燃料電極を順次積層した構造を有し、空気電極側から取り込まれた空気と燃料電極側から取り込まれた水素とが固体電解質を介して電気化学的に反応することにより起電力を生じるものである。そのため、固体電解質型燃料電池は環境及びエネルギーの両面から新しい発電システムとして期待され、既に燃料電池自動車などの分野で使用されている。 In general, a solid oxide fuel cell has a structure in which an air electrode made of porous LaMnO 3 or the like, a solid electrolyte having oxygen ion conductivity such as dense stabilized ZrO 2, and a fuel electrode made of NiO—ZrO 2 or the like are sequentially laminated. The air taken in from the air electrode side and the hydrogen taken in from the fuel electrode side react electrochemically through the solid electrolyte to generate an electromotive force. Therefore, the solid oxide fuel cell is expected as a new power generation system from the viewpoint of both environment and energy, and has already been used in the field of fuel cell vehicles and the like.
かかる固体電解質型燃料電池は、例えば平板タイプの場合、セルを支持する部分、一般的には電解質若しくは燃料電極をテープ成形若しくは押出成形により作製し、その上に他の構成部材のテープ成形品を重ねるか若しくはスラリーを塗布し、焼成することによって製造される。その際、製造工程を簡略化し且つ製造コストを低減するため、通常は各構成部材の少なくとも２つを同時に焼成する方法（共焼成法）がとられている。特に近年では、セル出力を向上させるため、電解質を薄くできる燃料電極支持型が注目されているが、支持体となる燃料電極の加熱収縮率が大きいため、特に共焼成法による焼成時に割れや剥離が生じたり、反りが発生したりするという問題があった。 In the case of such a solid electrolyte fuel cell, for example, in the case of a flat plate type, a portion that supports the cell, generally, an electrolyte or a fuel electrode is manufactured by tape molding or extrusion molding, and a tape molded product of other components is formed thereon. It is manufactured by stacking or applying a slurry and baking. At that time, in order to simplify the manufacturing process and reduce the manufacturing cost, a method (co-firing method) is generally employed in which at least two of the constituent members are simultaneously fired. In particular, in recent years, a fuel electrode support type that can make the electrolyte thinner is attracting attention in order to improve the cell output. However, since the heat shrinkage rate of the fuel electrode serving as the support is large, cracking and peeling are particularly caused during the co-firing method. There has been a problem of occurrence of warping and warping.
このような問題に対する解決策として、例えば、特開２００１−１８５１６０公報や特開２００１−１１８５８９公報には、固体電解質型燃料電池の厚みの調整や電極構造を工夫することで、焼成工程における各部材の収縮率の不整合による割れ、剥離、反りなどを抑制する方法が開示されている。しかし、これらの方法では、燃料電極の構成成分自体の加熱収縮については何ら改善ないし制御がなされていないうえ、各原料の選択幅が狭くなることや、製品構成の自由度が制限されるという問題があった。 As a solution to such a problem, for example, in Japanese Patent Laid-Open Nos. 2001-185160 and 2001-118589, each member in the firing step is devised by adjusting the thickness of the solid oxide fuel cell and devising the electrode structure. Disclosed is a method for suppressing cracks, peeling, warping, and the like due to mismatch in shrinkage. However, these methods do not improve or control the heat shrinkage of the components of the fuel electrode itself, and the selection range of each raw material is narrowed, and the degree of freedom of product configuration is limited. was there.
一方、固体電解質型燃料電池では、セル出力を向上させることが重要であり、そのため電極の抵抗値を低減することが求められている。このような要求に関連して、例えば、特開平１０−１４４３３７号公報には、安定化ジルコニアなどの酸化物の表面にニッケルなどの電極活性を有する金属を吸着させた燃料電極が記載され、好ましくは更にモリブデン、タングステン、白金のいずれか１種を添加することによって、電極中のニッケル同士の焼結を抑制し、電極構造の長期安定性を向上させる方法が記載されている。しかしながら、焼成時の収縮率の不整合による電極の割れや反りなどについては記載がないうえ、添加金属についても実施例にはモリブデンが記載されるのみであり、且つモリブデンなどの金属も相当多量の添加を必要としている。 On the other hand, in the solid oxide fuel cell, it is important to improve the cell output, and therefore it is required to reduce the resistance value of the electrode. In relation to such a requirement, for example, Japanese Patent Application Laid-Open No. 10-144337 describes a fuel electrode in which a metal having electrode activity such as nickel is adsorbed on the surface of an oxide such as stabilized zirconia. Describes a method of suppressing long-term stability of the electrode structure by further suppressing the sintering of nickel in the electrode by adding any one of molybdenum, tungsten, and platinum. However, there is no description about cracking or warping of the electrode due to mismatch of shrinkage rate at the time of firing, and only the molybdenum is described in the examples for the additive metal, and a considerable amount of metal such as molybdenum is also included. Needs addition.
また、特開平０９−２７４９２１号公報には、固体電解質型燃料電池の固体電解質の表面に、ニッケル又は酸化ニッケルの外層を設けたチタン又はタングステンの微粒子材料を付着させることによって、電極活性を向上させると共に、電解質と電極の膨張率の整合性を向上させることが記載されている。しかし、この発明は固体電解質の改良に関するものであるうえ、チタン又はタングステンの添加が電極の抵抗値に与える影響などについては記載されていない。 Japanese Patent Application Laid-Open No. 09-274921 improves the electrode activity by adhering a fine particle material of titanium or tungsten having an outer layer of nickel or nickel oxide to the surface of the solid electrolyte of the solid oxide fuel cell. In addition, it is described that the consistency between the expansion coefficient of the electrolyte and the electrode is improved. However, this invention relates to the improvement of the solid electrolyte and does not describe the influence of the addition of titanium or tungsten on the resistance value of the electrode.
更に、上記した特開平１０−１４４３３７号公報及び特開平０９−２７４９２１号公報の方法では、金属タングステンなどを使用するため、従来から大気中での焼成により作製している電極を不活性雰囲気中で焼成することが必要となり、焼成設備の改造や更新、不活性ガスの新たな消費などの点でコストが上昇するという問題がある。 Furthermore, in the methods disclosed in Japanese Patent Laid-Open Nos. 10-144337 and 09-274921, tungsten is used, so that an electrode that has been conventionally produced by firing in the atmosphere can be used in an inert atmosphere. There is a problem that it is necessary to calcinate, and the cost increases in terms of remodeling or renewal of calcination equipment, new consumption of inert gas, and the like.
本発明は、このような従来の事情に鑑み、固体電解質型燃料電池を製造する際の焼成工程において、構成部材間の加熱収縮率の不整合による割れや反りなどの発生を防止することができ、しかも燃料電池の抵抗値を低下させることが可能な、固体電解質型燃料電池の電極用酸化ニッケル粉及びその製造方法を提供することを目的とする。
In view of such conventional circumstances, the present invention can prevent the occurrence of cracks and warpage due to mismatching of the heat shrinkage rate between components in the firing step when manufacturing a solid oxide fuel cell. And it aims at providing the nickel oxide powder for electrodes of a solid oxide fuel cell which can reduce the resistance value of a fuel cell, and its manufacturing method.
本発明者らは、上記目的を達成するため鋭意研究を重ねた結果、固体電解質型燃料電池の燃料電極の構成成分として使用される酸化ニッケル（ＮｉＯ）について、一定の割合で酸化タングステン（ＷＯ３）を含有させることによって、高温で焼成したときの加熱収縮率を低減できること、更に酸化ニッケルとイットリア安定化ジルコニア（ＹＳＺ）などからなる燃料電極の抵抗値を低下できることを見出し、本発明をなすに至ったものである。 As a result of intensive studies to achieve the above object, the present inventors have found that tungsten oxide (WO 3 ) is used at a certain ratio with respect to nickel oxide (NiO) used as a component of the fuel electrode of the solid oxide fuel cell. ), The heat shrinkage rate when fired at high temperature can be reduced, and the resistance value of the fuel electrode composed of nickel oxide and yttria-stabilized zirconia (YSZ) can be reduced. It has come.
即ち、本発明が提供する固体電解質型燃料電池の電極用酸化ニッケル粉は、酸化ニッケルに対し０.０５重量％以上の酸化タングステンを含有することを特徴とするものである。また、この電極用酸化ニッケル粉は、加圧成形したペレットの１３５０℃での加熱収縮率が５〜１０％であることが好ましい。 That is, the nickel oxide powder for electrodes of a solid oxide fuel cell provided by the present invention is characterized by containing 0.05% by weight or more of tungsten oxide based on nickel oxide. Moreover, it is preferable that this nickel oxide powder for electrodes has a heat shrinkage rate of 5 to 10% at 1350 ° C. of the pressure-molded pellet.
本発明による固体電解質型燃料電池の電極用酸化ニッケル粉の製造方法は、酸化ニッケルに対し酸化タングステンが０.０５重量％以上となるように、酸化ニッケル粉と酸化タングステン粉を乾式若しくは湿式混合するか、又は乾式若しくは湿式混合の後に更に酸化雰囲気中にて３００〜１２００℃で焼成することを特徴とする。また、この電極用酸化ニッケル粉の製造方法においては、前記酸化タングステン粉の平均粒径が前記酸化ニッケル粉の平均粒径の５０％以下であることが好ましい。 In the method for producing nickel oxide powder for electrodes of a solid oxide fuel cell according to the present invention, nickel oxide powder and tungsten oxide powder are dry-type or wet-mixed so that tungsten oxide is 0.05% by weight or more with respect to nickel oxide. Or, after dry or wet mixing, firing at 300 to 1200 ° C. in an oxidizing atmosphere. In the method for producing nickel oxide powder for electrodes, it is preferable that the average particle diameter of the tungsten oxide powder is 50% or less of the average particle diameter of the nickel oxide powder.
本発明によれば、焼成工程における通常の加熱温度又はそれ以上の温度における燃料電極構成部材の加熱収縮率を、その構成成分である酸化ニッケルに酸化タングステンを添加することによって大幅に減少させることができる。従って、本発明の電極用酸化ニッケル粉を用いた燃料電極構成部材は、焼成工程において他の構成部材との収縮差が緩和され、共焼成法による焼成工程においても電極の割れ、剥離、反りなどを防止することができる。 According to the present invention, the heat shrinkage rate of the fuel electrode constituent member at a normal heating temperature or higher in the firing step can be greatly reduced by adding tungsten oxide to nickel oxide as its constituent component. it can. Therefore, the fuel electrode constituent member using the nickel oxide powder for electrodes of the present invention has a reduced shrinkage difference with other constituent members in the firing step, and cracks, delamination, warpage, etc. of the electrode also in the firing step by the co-firing method. Can be prevented.
また、本発明によれば、酸化タングステンの添加量によって燃料電極の抵抗値を従来に比べて大幅に低下させることが可能であり、その結果、好適な電極構造の形成と共に、セル出力を向上させることができる。しかも、酸化ニッケルに添加する酸化タングステンは、酸化物であって大気中で安定であるため、従来と同様に焼成工程を大気雰囲気中で行うことができる利点がある。 Further, according to the present invention, the resistance value of the fuel electrode can be greatly reduced as compared with the conventional case by the addition amount of tungsten oxide, and as a result, the cell output is improved with the formation of a suitable electrode structure. be able to. In addition, since tungsten oxide added to nickel oxide is an oxide and is stable in the air, there is an advantage that the firing step can be performed in the air as in the conventional case.
本発明の電極用酸化ニッケル粉中に含まれる酸化タングステンの量は、０.０５重量％以上必要であり、０.０５〜５重量％が好ましく、０.１〜３重量％が更に好ましい。電極用酸化ニッケル粉中の酸化タングステン含有量が０.０５重量％未満では、加熱収縮率の低減が十分でないため、特に共焼成時における構成部材間の収縮率を整合させる効果が少なく、燃料電極の抵抗値も十分に低下させることができない。また、酸化タングステン含有量が５重量％を超えても、加熱収縮率の更なる低減並びに燃料電極の抵抗値の更なる低下が見込めないうえ、コストアップを招く要因となる。 The amount of tungsten oxide contained in the nickel oxide powder for electrodes of the present invention is required to be 0.05% by weight or more, preferably 0.05 to 5% by weight, and more preferably 0.1 to 3% by weight. When the content of tungsten oxide in the nickel oxide powder for an electrode is less than 0.05% by weight, the reduction in heating shrinkage is not sufficient, so that there is little effect of matching the shrinkage between components particularly during co-firing. The resistance value cannot be reduced sufficiently. Further, even if the tungsten oxide content exceeds 5% by weight, further reduction of the heat shrinkage rate and further reduction of the resistance value of the fuel electrode cannot be expected, and this causes a cost increase.
更に詳しくは、酸化タングステンを０.０５重量％以上含有する本発明の電極用酸化ニッケル粉は、加圧成形したペレットで測定したとき、焼成工程で通常用いられる加熱温度又はそれ以上の加熱温度、例えば１３５０℃での加熱収縮率が５〜１０％となる。これに対して、酸化タングステンを含まない通常の酸化ニッケル粉では、同様に測定した加熱収縮率が１５％を超えている。この加熱収縮率を１０％以下に、即ち本発明における５〜１０％に低減することによって、他の電極構成部材との収縮差が緩和され、共焼成法による焼成工程においても、電極の割れ、剥離、反りなどを無くすことができる。 More specifically, the nickel oxide powder for an electrode of the present invention containing 0.05% by weight or more of tungsten oxide has a heating temperature usually used in the firing step or higher when measured with a pressure-molded pellet, For example, the heat shrinkage rate at 1350 ° C. is 5 to 10%. On the other hand, in the case of normal nickel oxide powder not containing tungsten oxide, the heat shrinkage rate similarly measured exceeds 15%. By reducing this heat shrinkage rate to 10% or less, that is, 5 to 10% in the present invention, the shrinkage difference with other electrode constituent members is alleviated, and even in the firing step by the co-firing method, the electrode cracks, Peeling and warping can be eliminated.
本発明における加熱収縮率の測定は、酸化ニッケル粉を圧力１ｔ／ｃｍ２で一軸加圧成形して直径５ｍｍの円柱状のペレットとし、このペレットについてＴＭＡ装置（例えば、ブルカーエイエックスエス社製、型式ＴＭＡ−４０００Ｓ）を用いて行った。具体的には、乾燥空気を０.３リットル／分で導入しながら、ペレットを１０℃／分の昇温速度で加熱し、１３５０℃にてペレットの厚さ方向における収縮率を測定した。 In the measurement of the heat shrinkage rate in the present invention, nickel oxide powder is uniaxially pressed at a pressure of 1 t / cm 2 to form a cylindrical pellet having a diameter of 5 mm. A TMA apparatus (for example, manufactured by Bruker AXS, Model TMA-4000S). Specifically, the pellet was heated at a heating rate of 10 ° C./min while introducing dry air at 0.3 liter / min, and the shrinkage rate in the thickness direction of the pellet was measured at 1350 ° C.
また、本発明の電極用酸化ニッケル粉を用いることにより、燃料電極の比抵抗を５％以上低下させることができる。例えば、酸化タングステンを約１重量％添加したとき、酸化タングステンを添加しない場合に対する比抵抗の低下率は約６０％で最大となる。尚、本発明における比抵抗の測定は、同一方法で作製した燃料電極の測定用試料を用い、直流四端子法により測定した。例えば、電極用酸化ニッケル粉とイットリア安定化ジルコニア（ＹＳＺ）からなる電極材料にエチルセルロースを添加混合し、円柱状のペレットに一軸加圧成形し、大気中で焼成した後、所定の直方体に切り出し、還元したものを測定用試料とする。 Moreover, the specific resistance of a fuel electrode can be reduced by 5% or more by using the nickel oxide powder for electrodes of the present invention. For example, when about 1% by weight of tungsten oxide is added, the rate of decrease in specific resistance with respect to the case where tungsten oxide is not added becomes maximum at about 60%. The specific resistance in the present invention was measured by a direct current four-terminal method using a fuel electrode measurement sample produced by the same method. For example, by adding and mixing ethyl cellulose to an electrode material consisting of nickel oxide powder for electrodes and yttria stabilized zirconia (YSZ), uniaxially press-molded into a cylindrical pellet, fired in the air, cut into a predetermined cuboid, The reduced sample is used as a measurement sample.
酸化タングステンの添加により燃料電極の比抵抗が低下する理由は、次のように考えられる。酸化タングステンは絶縁体であり、通常であれば添加することで抵抗値が増大する。しかし、電極製造工程での水素還元において、酸化ニッケルが金属ニッケルになると同時に、酸化タングステンも各種の中間酸化物を経て金属タングステンとなり、導電性（Ｗの比抵抗：５.６５×１０−６Ωｃｍ）を発現するものと考えられる。ところが、酸化タングステンの添加量が２重量％を超えると、通常の還元処理を行っても未反応の酸化タングステンが残るため、比抵抗が再び上昇するものと考えられる。尚、１００％水素気流中などの強還元雰囲気で還元すれば、酸化タングステンの添加量が多くても比抵抗が低下する可能性があるが、コストアップを招くため、酸化タングステンの添加は５重量％以下とすることがより望ましい。 The reason why the specific resistance of the fuel electrode is reduced by the addition of tungsten oxide is considered as follows. Tungsten oxide is an insulator, and the resistance value is increased by adding it normally. However, in the hydrogen reduction in the electrode manufacturing process, nickel oxide is converted into metallic nickel, and at the same time, tungsten oxide is converted into metallic tungsten through various intermediate oxides, and conductivity (specific resistance of W: 5.65 × 10 −6 Ωcm). ). However, if the added amount of tungsten oxide exceeds 2% by weight, it is considered that the specific resistance rises again because unreacted tungsten oxide remains even if a normal reduction treatment is performed. If the reduction is performed in a strong reducing atmosphere such as in a 100% hydrogen stream, the specific resistance may decrease even if the amount of tungsten oxide added is large. However, since the cost is increased, the addition of tungsten oxide is 5% by weight. % Or less is more desirable.
本発明による電極用酸化ニッケル粉の製造方法は、酸化ニッケル（ＮｉＯ）と酸化タングステン（ＷＯ３）を共存させることができれば、如何なる方法であってもよい。最も簡単な方法としては、酸化ニッケル粉と酸化タングステン粉を所定割合（ＷＯ３／ＮｉＯ＝０.０５〜５重量％）となるように乾式混合する方法がある。また、水あるいはアルコールなどの有機溶媒を用いて湿式混合する方法も簡単であり、より微細で且つ均一な粉末が得られる利点がある。尚、酸化ニッケル粉と酸化タングステン粉の乾式混合にはブレンダー、ミキサー、ボールミルなどが好適に使用でき、湿式混合にはボールミル、ディスクミル、ビーズミル、ミキサーなどが好適に使用できる。 The method for producing the nickel oxide powder for electrodes according to the present invention may be any method as long as nickel oxide (NiO) and tungsten oxide (WO 3 ) can coexist. As the simplest method, there is a method in which nickel oxide powder and tungsten oxide powder are dry-mixed so as to have a predetermined ratio (WO 3 /NiO=0.05 to 5% by weight). In addition, the wet mixing method using an organic solvent such as water or alcohol is simple, and there is an advantage that a finer and more uniform powder can be obtained. In addition, a blender, a mixer, a ball mill, etc. can be used conveniently for dry mixing of nickel oxide powder and tungsten oxide powder, and a ball mill, a disk mill, a bead mill, a mixer, etc. can be used suitably for wet mixing.
これらの方法により得られる電極用酸化ニッケル粉が、上記した加熱収縮率の低減及び抵抗値の低下について十分効果を発揮するためには、酸化タングステンと酸化ニッケルが均一に混合されていることが必要である。そのためには、乾式混合であるか湿式混合であるかにかかわらず、使用する酸化タングステン粉の平均粒径が、酸化ニッケル粉の平均粒径と同等以下であることが望ましく、更には酸化ニッケル粉の平均粒径の５０％以下であることが好ましい。 In order for the nickel oxide powder for electrodes obtained by these methods to sufficiently exhibit the effects of the above-described reduction of the heat shrinkage rate and the resistance value, it is necessary that tungsten oxide and nickel oxide are uniformly mixed. It is. For this purpose, it is desirable that the average particle diameter of the tungsten oxide powder used is equal to or less than the average particle diameter of the nickel oxide powder, regardless of whether it is dry mixing or wet mixing. The average particle size is preferably 50% or less.
上記の乾式混合又は湿式混合により混合した酸化ニッケル粉と酸化タングステン粉は、更に空気などの酸化雰囲気中において焼成することもできる。特に、酸化ニッケル粉の代わりに、その前駆体である水酸化ニッケルを用いることも可能であるが、その場合には乾式混合又は湿式混合の後に、酸化雰囲気中にて３００℃以上で焼成して水酸化ニッケルを酸化ニッケルとする必要がある。尚、上記焼成には、マッフル炉、管状炉、ポット炉、転動炉、プッシャ-炉、バーナー炉などの一般的な焼成炉が使用できる。 The nickel oxide powder and the tungsten oxide powder mixed by the above dry mixing or wet mixing can be further fired in an oxidizing atmosphere such as air. In particular, it is possible to use nickel hydroxide as a precursor instead of nickel oxide powder. In that case, after dry mixing or wet mixing, firing is performed at 300 ° C. or higher in an oxidizing atmosphere. Nickel hydroxide needs to be nickel oxide. For the firing, a general firing furnace such as a muffle furnace, a tubular furnace, a pot furnace, a rolling furnace, a pusher furnace, and a burner furnace can be used.
また、上記焼成時の温度としては、３００℃以上が必要であるが、１２００℃を超えると酸化ニッケルの焼結が進むと共に粒成長して、粗大な粒子となるため好ましくない。従って、固体電解質型燃料電池用の電極に好適に使用できる酸化ニッケル粉は、空気などの酸化雰囲気中において３００〜１２００℃で焼成することが好ましい。ただし、焼成条件によっては酸化ニッケルが焼結して粒成長や二次粒子を形成するため、求める酸化ニッケル粉の特性に応じて望ましい焼成条件を定める必要がある。また、焼結した粒子を再粉砕することで、燃料電極用材料として利用することも可能である。 Further, the temperature at the time of firing is required to be 300 ° C. or higher. However, if it exceeds 1200 ° C., the sintering of nickel oxide proceeds and the grains grow to become coarse particles, which is not preferable. Therefore, the nickel oxide powder that can be suitably used for the electrode for the solid oxide fuel cell is preferably fired at 300 to 1200 ° C. in an oxidizing atmosphere such as air. However, since nickel oxide sinters to form grain growth and secondary particles depending on the firing conditions, it is necessary to determine desirable firing conditions according to the characteristics of the nickel oxide powder desired. Further, the sintered particles can be used as a fuel electrode material by re-grinding.
本発明の電極用酸化ニッケル粉は、従来と同様に固体電解質型燃料電池を製造する際に、イットリア安定化ジルコニア（ＹＳＺ）などの他の構成成分と混練して、燃料電極用のスラリーとして使用する。電極用酸化ニッケル粉とＹＳＺとの混合粉中における酸化ニッケル粉の割合は、一般的に５０〜７０重量％が好ましい。尚、ＹＳＺの代わりに、スカンジア安定化ジルコニアやセリアなど、他の酸素イオン伝導体を用いることもできる。 The nickel oxide powder for electrodes of the present invention is used as a slurry for fuel electrodes by kneading with other components such as yttria stabilized zirconia (YSZ) when producing a solid oxide fuel cell as in the conventional case. To do. The proportion of nickel oxide powder in the mixed powder of nickel oxide powder for electrodes and YSZ is generally preferably 50 to 70% by weight. Instead of YSZ, other oxygen ion conductors such as scandia-stabilized zirconia and ceria can also be used.
例えば、上記電極用酸化ニッケル粉をＹＳＺなどの他の構成成分と混練したスラリーを用い、燃料電極構成部材を押出成形により作製する。その上に固体電解質や空気電極など他の構成部材のスラリーを塗布し、これらを共焼成法により同時に焼成する。その際に、本発明の電極用酸化ニッケル粉を用いることで、焼成時における燃料電極層と他の層との収縮差が緩和され、電極の割れ、剥離、反りなどを防止することができる。また、焼成で形成される燃料電極の抵抗値が低下し、セル出力を向上させることができる。 For example, a fuel electrode constituent member is produced by extrusion molding using a slurry obtained by kneading the nickel oxide powder for an electrode with other constituents such as YSZ. A slurry of another constituent member such as a solid electrolyte or an air electrode is applied thereon, and these are simultaneously fired by a co-firing method. At that time, by using the nickel oxide powder for an electrode of the present invention, the difference in shrinkage between the fuel electrode layer and other layers during firing is alleviated, and cracking, peeling, warping, etc. of the electrode can be prevented. Moreover, the resistance value of the fuel electrode formed by firing is reduced, and the cell output can be improved.
尚、本発明による電極用酸化ニッケル粉は、固体電解質型燃料電池の電極以外にも、水素生成用の触媒や水素センサー材料などの電子デバイス材料としても利用することができる。 The nickel oxide powder for electrodes according to the present invention can be used as an electronic device material such as a catalyst for hydrogen generation and a hydrogen sensor material in addition to the electrode of the solid oxide fuel cell.
平均一次粒径が０.６μｍの酸化ニッケル粉と平均粒径が０.２μｍの酸化タングステン粉を、直径２ｍｍの部分安定化ジルコニア（ＰＳＺ）ボールを用いたボールミルにより、エタノールを溶媒として湿式混合した。得られた混合粉を１０５℃の大気乾燥機で乾燥させた後、解砕して電極用酸化ニッケル粉を作製した。その際、酸化ニッケル粉に対する酸化タングステン粉の添加量を、０〜５重量％の範囲で下記表１に示すように変化させた。 Nickel oxide powder having an average primary particle size of 0.6 μm and tungsten oxide powder having an average particle size of 0.2 μm were wet mixed using ethanol as a solvent by a ball mill using partially stabilized zirconia (PSZ) balls having a diameter of 2 mm. . The obtained mixed powder was dried with an air dryer at 105 ° C., and then crushed to produce nickel oxide powder for electrodes. At that time, the addition amount of the tungsten oxide powder with respect to the nickel oxide powder was changed in the range of 0 to 5% by weight as shown in Table 1 below.
得られた各電極用酸化ニッケル粉について、加熱収縮率と燃料電極としたときの抵抗値を下記する方法により測定し、その結果を表１に併せて示した。即ち、加熱収縮率については、電極用酸化ニッケル粉を圧力１ｔ／ｃｍ２で直径５ｍｍの円柱状ペレットに一軸加圧成形し、ＴＭＡ装置（ブルカーエイエックスエス社製、型式ＴＭＡ−４０００Ｓ）により、１３５０℃でのペレットの厚さ方向の加熱収縮率を測定した。 About each obtained nickel oxide powder for electrodes, the heat shrinkage rate and the resistance value when used as a fuel electrode were measured by the following methods, and the results are also shown in Table 1. That is, for the heat shrinkage rate, the nickel oxide powder for electrodes was uniaxially pressed into a cylindrical pellet having a diameter of 5 mm at a pressure of 1 t / cm 2 , and the TMA apparatus (Bruker AXS, model TMA-4000S) was used. The heat shrinkage rate in the thickness direction of the pellet at 1350 ° C. was measured.
また、燃料電極の比抵抗に関しては、以下の手順で測定した。まず、電極用酸化ニッケル粉とＹＳＺとを重量比で６５：３５となるように秤量し、乳鉢で均一に混合した後、混合粉全量に対して５重量％のエチルセルロースをバインダーとして添加混合した。この粉末を圧力２００ｋｇ／ｃｍ２で直径２５ｍｍの円柱状ペレットに一軸加圧成形し、大気中において１５００℃で３時間焼成した。次に、得られた焼結体を縦横２.５ｍｍ×厚さ２０ｍｍの直方体に切り出し、４％Ｈ２／Ｎ２雰囲気下にて９５０℃で３時間の還元処理を施し、これに４本の導線を取り付けた。得られた燃料電極について、直流四端子法により、室温の大気雰囲気中と、９００℃の４％Ｈ２／Ｎ２雰囲気中において、ポテンショ・ガルバノスタット（ソーラトロン社製、型式ＳＩ−１２８７）を用いて導電率を測定し、比抵抗を求めた。 Further, the specific resistance of the fuel electrode was measured by the following procedure. First, the nickel oxide powder for electrodes and YSZ were weighed so as to have a weight ratio of 65:35, and uniformly mixed in a mortar, and then 5% by weight of ethylcellulose was added and mixed as a binder with respect to the total amount of the mixed powder. This powder was uniaxially pressed into a cylindrical pellet having a diameter of 25 mm at a pressure of 200 kg / cm 2 and fired at 1500 ° C. for 3 hours in the air. Next, the obtained sintered body was cut into a rectangular parallelepiped having a length and width of 2.5 mm and a thickness of 20 mm, and subjected to reduction treatment at 950 ° C. for 3 hours in a 4% H 2 / N 2 atmosphere. A conductor was attached. About the obtained fuel electrode, a potentio galvanostat (manufactured by Solartron, model SI-1287) was used by a direct current four-terminal method in an air atmosphere at room temperature and in a 4% H 2 / N 2 atmosphere at 900 ° C. The electrical conductivity was measured to determine the specific resistance.
上記の結果から分かるように、加熱収縮率は酸化タングステンの添加によって明らかに低減され、酸化タングステンの添加量が０.１〜２重量％の範囲で約６〜８％と１０％以下の加熱収縮率であり、添加量が３重量％の試料７で加熱収縮率が最も小さくなった。 As can be seen from the above results, the heat shrinkage rate is obviously reduced by the addition of tungsten oxide, and the heat shrinkage is about 6-8% and less than 10% in the range of 0.1-2% by weight of tungsten oxide addition. The rate of heat shrinkage was the smallest in sample 7 with an addition amount of 3 wt%.
一方、燃料電極の動作温度に近い９００℃での比抵抗は、酸化タングステンを添加していない試料１が７８８μΩｃｍであるのに対して、酸化タングステンの添加量が増えるに伴って低下し、添加量が１重量％の試料５で３１８μΩｃｍと最も低くなったが、これは試料１に対して約６０％の低下に相当する。更に酸化タングステンの添加量を増やすと、比抵抗は再び上昇し始めるが、添加量が５重量％の試料８でも無添加の場合より低い比抵抗を示した。
On the other hand, the specific resistance at 900 ° C., which is close to the operating temperature of the fuel electrode, is 788 μΩcm for the sample 1 to which no tungsten oxide is added, whereas it decreases as the amount of tungsten oxide added increases. Was the lowest at 318 μΩcm in the sample 5 of 1% by weight, which corresponds to a decrease of about 60% with respect to the sample 1. When the addition amount of tungsten oxide was further increased, the specific resistance started to increase again, but the sample 8 having an addition amount of 5% by weight showed a lower specific resistance than that in the case of no addition.
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