JP3638489B2

JP3638489B2 - Solid oxide fuel cell

Info

Publication number: JP3638489B2
Application number: JP36793599A
Authority: JP
Inventors: 雅人西原; 高志重久
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 1999-12-24
Filing date: 1999-12-24
Publication date: 2005-04-13
Anticipated expiration: 2019-12-24
Also published as: JP2001185160A

Description

【０００１】
【発明の属する技術分野】
本発明は、空気極の表面に、固体電解質、燃料極を順次積層してなる固体電解質型燃料電池セルに関するものである。
【０００２】
【従来技術】
従来より、固体電解質型燃料電池はその作動温度が９００〜１０５０℃と高温であるため発電効率が高く、第３世代の発電システムとして期待されている。
【０００３】
一般に固体電解質型燃料電池セルには、円筒型と平板型が知られている。平板型燃料電池セルは、発電の単位体積当たり出力密度は高いという特徴を有するが、実用化に関してはガスシール不完全性やセル内の温度分布の不均一性などの問題がある。それに対して、円筒型燃料電池セルでは、出力密度は低いものの、セルの機械的強度が高く、またセル内の温度の均一性が保てるという特徴がある。両形状の固体電解質型燃料電池セルとも、それぞれの特徴を生かして積極的に研究開発が進められている。
【０００４】
円筒型燃料電池の単セルは、図６に示したように開気孔率３０〜４０％程度のＬａＭｎＯ₃系材料からなる多孔性の空気極支持管２を形成し、その表面にＹ₂Ｏ₃安定化ＺｒＯ₂からなる固体電解質３を被覆し、さらにこの表面に多孔性のＮｉ−ジルコニアの燃料極４が設けられている。燃料電池のモジュールにおいては、各単セルはＬａＣｒＯ₃系の集電体（インターコネクタ）５を介して接続される。発電は、空気極支持管２内部に空気（酸素）６を、外部に燃料（水素）７を流し、１０００〜１０５０℃の温度で行われる。
【０００５】
上記のような燃料電池セルを製造する方法としては、例えばＣａＯ安定化ＺｒＯ₂からなる絶縁粉末を押出成形法などにより円筒状に成形後、これを焼成して円筒状支持体を作製し、この支持体の外周面に空気極、固体電解質、燃料極、集電体のスラリーを塗布してこれを順次焼成して積層するか、あるいは円筒状支持体の表面に電気化学的蒸着法（ＥＶＤ法）やプラズマ溶射法などにより空気極、固体電解質、燃料極、集電体を順次形成することも行われている。
【０００６】
近年ではセルの製造工程を簡略化し且つ製造コストを低減するために、各構成材料のうち少なくとも２つを同時焼成する、いわゆる共焼結法が提案されている。この共焼結法は、例えば、円筒状の空気極成形体に固体電解質成形体及び集電体成形体をロール状に巻き付けて同時焼成を行い、その後、固体電解質層表面に燃料極層を形成する方法である。またプロセス簡略化のために、固体電解質成形体の表面にさらに燃料極成形体を積層して、同時焼成する共焼結法も提案されている。
【０００７】
この共焼結法は非常に簡単なプロセスで製造工程数も少なく、セルの製造時の歩留まり向上、コスト低減に有利である。このような共焼結法による燃料電池セルでは、Ｙ₂Ｏ₃安定化または部分安定化ＺｒＯ₂からなる固体電解質を用い、この固体電解質に熱膨張係数を合致させる等のため、空気極材料として、ＬａＭｎＯ₃からなるペロブスカイト型複合酸化物のＬａの一部をＹおよびＣａで置換したものが用いられている（特開平１０−１６２８４７号公報等参照）。
【０００８】
【発明が解決しようとする課題】
しかしながら、円筒状の空気極成形体に、固体電解質成形体、燃料極成形体を積層し、共焼結法を用いて円筒型燃料電池セルを作製すると、焼結後において燃料極自体が剥離したり、燃料極と固体電解質との焼成収縮差が大きいことに基づき、発電性能が悪化するという問題があった。
【０００９】
即ち、従来、共焼結法においては、燃料極の厚みが最適化されておらず、例えば、燃料極成形体の厚みが厚い場合には、燃料極と固体電解質での熱膨張率の不具合を緩和できずに、焼結後に燃料極自体が剥離するという問題があった。
【００１０】
また、燃料極成形体の厚みが薄い場合には、固体電解質成形体のセル長さ方向の端面に対して、燃料極成形体のセル長さ方向の端面を合致させて積層しても、焼結後には、燃料極の端面が固体電解質の端面から大きく内方へ移動し、即ち、燃料極が固体電解質に対して大きく収縮し、その界面組織を観察すると、燃料極と固体電解質との界面から固体電解質内部へ向かってクラック（亀裂）が進行しており、この結果、燃料ガスが漏出したり、また、発電性能上の観点からは、上記収縮差が大きくなるにつれ、燃料極サイトの分極値、およびセル構成成分の実抵抗値が初期段階から高くなるという問題があった。
【００１１】
本発明は、燃料極の剥離を防止できるとともに、燃料極と固体電解質との焼成収縮差を小さくして、発電性能を向上できる固体電解質型燃料電池セルを提供することを目的とする。
【００１２】
【課題を解決するための手段】
本発明の固体電解質型燃料電池セルは、空気極成形体（仮焼したものも包含する意味である）上に第１固体電解質成形体を積層し、該第１固体電解質成形体（仮焼したものも包含する意味である）上に、燃料極成形体が積層された第２固体電解質成形体を、前記第１固体電解質成形体と前記第２固体電解質成形体が当接するように積層し、同時焼成してなるとともに、燃料極の厚みが５〜２０μｍであることを特徴とする。
【００１３】
このような構成を採用することにより、空気極成形体、固体電解質成形体、燃料極成形体を順次積層し、同時焼成したとしても、部材間に発生する焼成収縮率差に伴う応力を緩和できるため、固体電解質からの燃料極の剥離を防止できるとともに、燃料極と固体電解質との焼成収縮差を小さくできる。
【００１４】
このように、燃料極と固体電解質との焼成収縮差を小さくできるため、固体電解質と燃料極の界面から固体電解質内部に生成するクラック（亀裂）を阻止することが可能となる。その結果、燃料極と固体電解質間の分極値の増大、また固体電解質成分の実抵抗値の増大を防止でき、これに伴い初期の高い出力密度を長期的に亘って維持できる。
【００１６】
例えば、空気極成形体の表面に形成されたＺｒＯ₂を含有する第１固体電解質成形体に、ＺｒＯ₂を含有する第２固体電解質成形体と金属粒子を含有する燃料極成形体との積層体からなるシート状の積層成形体を、第１固体電解質成形体に前記第２固体電解質成形体が当接するように積層した後、焼成する。
【００１７】
このように、第２固体電解質成形体と燃料極成形体とのシート状の積層成形体を作製した後、この積層成形体を、第１固体電解質成形体に第２固体電解質成形体が当接するように積層したので、焼成すると燃料極と固体電解質とを強固に接合でき、燃料極の固体電解質からの剥離を防止できる。
【００１８】
さらに、燃料極と固体電解質との焼成収縮差を小さくして、固体電解質の端面と燃料極の端面との間隔を０．１５ｍｍ以下とすることが望ましい。
【００１９】
また、燃料極が金属粒子とＺｒＯ₂粒子を含有するとともに、燃料極が、固体電解質側の第１燃料極層と、該第１燃料極層の表面に形成された第２燃料極層とからなり、前記第１燃料極層のＺｒＯ₂粒子の平均粒径を、前記第２燃料極層のＺｒＯ₂粒子の平均粒径よりも小さくすることが望ましい。
【００２０】
これは、第１燃料極層の微粒なＺｒＯ₂粒子により、金属粒子の周りを十分に支持して、燃料極の金属粒子の粒成長を抑制し、燃料極の金属粒子と固体電解質との接触点を多くすることができ、燃料極サイトの分極値を小さくできるとともに、第２燃料極層の平均粒径が大きいＺｒＯ₂粒子により、燃料極の焼成収縮を小さくすることができ、燃料極と固体電解質との焼成収縮差を小さくできる。
【００２１】
即ち、燃料極を構成する金属粒子、ＺｒＯ₂粒子の平均粒径においては、ＺｒＯ₂粒子の平均粒径が小さいほど、金属粒子の粒成長抑制のための骨格を形成し易く、金属粒子の粒成長抑制効果が大きい。一方、ＺｒＯ₂粒子の平均粒径が大きいほど、燃料極の焼成収縮が小さくなり、固体電解質に近づくためである。
【００２２】
特に、第１燃料極層のＺｒＯ₂粒子の平均粒径が０．８μｍ以下であり、第２燃料極層のＺｒＯ₂粒子の平均粒径が１μｍ以上であることが望ましい。
【００２３】
【発明の実施の形態】
本発明における固体電解質型燃料電池セルは、例えば、図１に示すように円筒状の固体電解質３１の内面に空気極３２、外面に燃料極３３を形成してセル本体３４を形成し、空気極３２には集電体３５（インターコネクタ）が電気的に接続されている。
【００２４】
即ち、固体電解質３１の一部に切欠部３６が形成され、固体電解質３１の内面に形成されている空気極３２の一部が露出しており、この露出面３７及び切欠部３６近傍の固体電解質３１の表面が集電体３５により被覆され、集電体３５が、固体電解質３１の両端部表面及び固体電解質３１の切欠部３６から露出した空気極３２の表面に接合されている。
空気極３２と電気的に接続する集電体３５は、セル本体３４の外面に形成され、ほぼ段差のない連続同一面３９を覆うように形成されており、燃料極３３とは電気的に接続されていない。この集電体３５は、セル同士間を接続する際に他のセルの燃料極にＮｉフェルトを介して電気的に接続され、これにより燃料電池モジュールが構成される。連続同一面３９は、固体電解質の両端部と空気極の一部とが連続したほぼ同一面となるまで、固体電解質の両端部間を研磨することにより形成される。
固体電解質３１は、例えば３〜１５モル％のＹ₂Ｏ₃を含有した部分安定化あるいは安定化ＺｒＯ₂が用いられる。また、空気極３２としては、例えば、主としてＬａをＣａ又はＳｒで１０〜２０原子％置換したＬａＭｎＯ₃が用いられ、集電体３５としては、例えば、主としてＣｒをＭｇで１０〜３０原子％置換したＬａＣｒＯ₃が用いられる。燃料極３３としては、５０〜８０重量％のＮｉを含むＺｒＯ₂（Ｙ₂Ｏ₃含有）サーメットが用いられる。固体電解質３１、空気極３２、集電体３５、燃料極３３としては、上記例に限定されるものではなく、公知材料を用いても良い。
そして、本発明の固体電解質型燃料電池セルは、固体電解質３１は、空気極３２表面に形成された第１固体電解質３１ａと、この第１固体電解質３１ａの表面に形成された第２固体電解質３１ｂとから構成され、この第２固体電解質３１ｂの表面に燃料極３３が形成されており、燃料極３３の厚みが５〜２０μｍとされている。
【００２５】
燃料極３３の厚みを５〜２０μｍと設定したのは、燃料極３３の厚みが５μｍより小さいと、Ｎｉ粒子の粒成長に伴い焼成時の収縮量が増大し、一方、２０μｍより大きいと、共焼結を行った後に、燃料極３３と固体電解質３１間での熱膨張率の不具合を緩和できずに、燃料極３３自体が剥離するからである。燃料極３３の収縮量を小さくし、かつ燃料極３３の剥離を防止するという点から、燃料極３３の厚みは１０〜２０μｍが望ましい。
【００２６】
燃料極３３は、ＺｒＯ₂粒子の平均粒径は０．４〜０．８μｍとされ、Ｎｉ粒子の平均粒径は０．２〜０．６μｍとされている。ＺｒＯ₂粒子の平均粒径が０．４μｍよりも小さい場合には、固体電解質との焼成収縮差が顕著に発生する傾向があり、また、Ｎｉ粒子の平均粒径が０．６μｍよりも大きい場合には、ＮｉおよびＺｒＯ₂粒子間の接触点の増大を図れなくなる傾向があるからである。また、Ｎｉ粒子の平均粒径が０．２μｍよりも小さい場合には、ＺｒＯ₂粒子との均一混合が困難で、逆に凝集を伴う傾向があり、ＺｒＯ₂粒子の平均粒径が０．８μｍよりも大きい場合には、Ｎｉ粒子の周りの均一な支持が図れない傾向があるからである。
【００２７】
図２は、本発明の固体電解質型燃料電池セルの斜視図であり、図３は、燃料極３３と固体電解質３１の境界近傍を拡大して示す正面図である。この図３に示すように、本発明の固体電解質型燃料電池セルでは、セル長さ方向の燃料極３３の端面Ａと、その下面に形成された固体電解質３１のセル長さ方向の端面Ｂとの間隔ｘが０．１５ｍｍ以下とされている。端面Ａと端面Ｂとの間隔ｘが０．１５ｍｍよりも大きい場合には、燃料極３３と固体電解質３１（第１固体電解質３１ａ）の焼成収縮差が大きく、固体電解質３１にクラックが生成する傾向があるからである。端面Ａと端面Ｂとの間隔ｘは、固体電解質３１におけるクラック生成防止という点から、０．１０ｍｍ以下であることが望ましい。
【００２８】
本発明の固体電解質型燃料電池セルは、まず、円筒状の空気極成形体を形成する。この円筒状の空気極成形体は、例えば所定の調合組成に従いＬａ₂Ｏ₃、Ｙ₂Ｏ₃、ＣａＯ、ＭｎＯ₂の素原料を秤量、混合した後、１５００℃程度の温度で２〜１０時間仮焼し、その後４〜８μｍの粒度に粉砕調製する。
【００２９】
調製した粉体に、バインダーを混合、混練し押出成形法により円筒状の空気極成形体を作製し、さらに脱バインダー処理し、１２００〜１２５０℃で仮焼を行うことで円筒状の空気極仮焼体を作製する。
【００３０】
シート状の第１固体電解質成形体として、所定粉末にトルエン、バインダー、市販の分散剤を加えてスラリー化したものをドクターブレード等の方法により、例えば、１００〜１２０μｍの厚さに成形したものを用い、円筒状の空気極仮焼体の表面に第１固体電解質成形体を貼り付けて仮焼する。
【００３１】
次に、シート状の燃料極成形体を作製する。まず、例えば、所定比率に調製したＮｉＯ／ＹＳＺ混合粉体にトルエン、バインダーを加えてスラリー化したものを準備する。前記第１固体電解質成形体の作製と同様、成形、乾燥し、例えば、１５μｍの厚さのシート状の第２固体電解質成形体を形成する。
【００３２】
この第２固体電解質成形体上に燃料極層成形体を印刷、乾燥した後、図４に示すように、第１固体電解質仮焼体５３上に、燃料極層成形体５４が形成された第２固体電解質成形体５５を、第１固体電解質仮焼体５３に第２固体電解質成形体５５が当接するように巻き付け、積層する。尚、符号５１は空気極仮焼体である。
【００３３】
燃料極層成形体の厚みは９〜６０μｍの厚みとされている。燃料極層成形体の厚みが９μｍよりも薄くなると、Ｎｉ粒成長に伴い焼成収縮差が助長され、一方６０μｍよりも厚くなると、固体電解質間との熱膨張率の不整合を伴って燃料極が剥離し易くなる。このような点から、燃料極成形体の厚みは特に２５〜４０μｍが望ましい。
【００３４】
燃料極層成形体を構成するＮｉ／ＹＳＺ混合粉体は、Ｎｉ粉末の平均粒径が０．２〜０．６μｍ、ＹＳＺ粉末の平均粒径が０．４〜０．８μｍの原料粉体を用い、所定比率に調合した後分散性を高めるためにＺｒＯ₂ボールを用いて湿式粉砕混合を行う。燃料極を構成するＹＳＺ粉末の粒子径が０．８μｍよりも大きくなると、焼成収縮差という点では問題無いが、Ｎｉ粒子の支持がミクロレベルで十分でないために局所的にＮｉ粒成長を伴う。
【００３５】
さらに、燃料極を構成するＮｉ粉末とＹＳＺ粉末との各粒径の組合わせにおいても、焼成収縮差の低減は可能である。ＹＳＺ粉末が０．８μｍ以上の粒径になると焼成時の収縮差という観点では問題無いが、Ｎｉ粒子の粒成長を抑制できずに、その結果反応サイト数の減少に因る燃料極サイトの分極増大を伴って出力性能が低下する。
【００３６】
その結果、反応サイト数という観点においてＮｉ／ＹＳＺ間の接点数が減少し、そのために燃料極サイトの分極値が極めて増大し出力性能が低下する。また、Ｎｉ含有比率が８０％より高くなると、固体電解質膜との熱膨張率の不整合を生じ易く剥離が生じ易い。
【００３７】
次に、固体電解質成形体の調製同様、１００〜１２０μｍの厚さに成形した集電体成形体を所定箇所に貼り付ける。
【００３８】
この後、円筒状空気極成形体５１、固体電解質成形体５３、５５、燃料極成形体５４および集電体成形体の積層体は、大気中１４００〜１５５０℃の温度で、４層同時に共焼成される。
【００３９】
以上のように構成された固体電解質型燃料電池セルでは、空気極成形体、固体電解質成形体、燃料極成形体を順次積層し、同時焼成したとしても、部材間に発生する焼成収縮量、熱膨張差に伴う反応を緩和できるため、固体電解質からの燃料極の剥離を防止できるとともに、燃料極と固体電解質との焼成収縮差を小さくでき、これにより、固体電解質内部に生成するクラックを阻止することができ、その結果、燃料極と固体電解質間の分極値の増大、また固体電解質成分の実抵抗値の増大を防止でき、初期の高い出力密度を長期的に亘って維持できる。
【００４０】
また、固体電解質成形体の表面に燃料極成形体を巻き付けて積層するのではなく、第２固体電解質成形体と燃料極成形体とのシート状の積層成形体を作製した後、この積層成形体を、第１固体電解質成形体に第２固体電解質成形体が当接するように積層したので、燃料極と固体電解質とを強固に接合でき、燃料極の固体電解質からの剥離を防止できる。
【００４１】
また、図５は、本発明の他の固体電解質型燃料電池セルを示すもので、この例では、燃料極３３を、固体電解質側の第１燃料極層３３ａと、外面側の第２燃料極層３３ｂとから構成し、第１燃料極層３３ａのＺｒＯ₂粒子の平均粒径を、第２燃料極層３３ｂのＺｒＯ₂粒子の平均粒径よりも小さくされている。ここでは、第１燃料極層３３ａのＺｒＯ₂粒子の平均粒径が０．８μｍ以下とされ、第２燃料極層３３ｂのＺｒＯ₂粒子の平均粒径が１μｍ以上とされ、他の構成は上記例と同一である。
【００４２】
ここで、第１燃料極層３３ａのＺｒＯ₂粒子を平均粒径が０．８μｍ以下にしたのは、第１燃料極層の微粒なＺｒＯ₂粒子により、金属粒子（Ｎｉ）の回りを十分に支持して、燃料極の金属粒子の粒成長を抑制し、燃料極３３の金属粒子と固体電解質３１との接触点を多くすることができるからである。
【００４３】
また、第２燃料極層３３ｂのＺｒＯ₂粒子の平均粒径が１μｍ以上としたのは、第２燃料極層３３ｂの平均粒径が大きいＺｒＯ₂粒子により、燃料極３３の焼成収縮を小さくすることができ、燃料極３３と固体電解質３１との焼成収縮差を小さくできるからである。尚、燃料極の金属粒子は、焼成温度で粒成長するものの、ＺｒＯ₂粒子は殆ど粒成長しない。
【００４４】
このような固体電解質型燃料電池セルは、第２固体電解質成形体の表面に第１燃料極層成形体を印刷、乾燥した後、第１燃料極層成形体上に第２燃料極層成形体を印刷、乾燥し、この積層成形体を第１固体電解質仮焼体の表面に積層する以外は、上記と同様に製造することができる。
【００４５】
尚、上記例では、円筒型の固体電解質型燃料電池セルについて説明したが、平板型燃料電池セルであっても良い。
【００４６】
また、上記例では、空気極成形体および第１固体電解質成形体を一旦仮焼し、これに第２固体電解質成形体、燃料極成形体を形成したが、仮焼することなく、空気極成形体に第１固体電解質成形体、第２固体電解質成形体、燃料極成形体を形成しても良い。
【００４７】
【実施例】
実施例１
円筒状固体電解質型燃料電池セルを共焼結法により作製するため、まず円筒状の空気極成形体を以下の手順で作製した。
【００４８】
市販の純度９９．９％以上のＬａ₂Ｏ₃、Ｙ₂Ｏ₃、ＣａＣＯ₃、Ｍｎ₂Ｏ₃を出発原料として、Ｌａ_0.56Ｙ_0.14Ｃａ_0.3ＭｎＯ₃の組成になるように秤量し、これに有機バインダーを添加し、押出成形し、脱バイ・仮焼により空気極仮焼体を形成した。
【００４９】
次に、Ｙ₂Ｏ₃を８モル％の割合で含有する平均粒径が１〜２μｍのＺｒＯ₂粉末を用いてスラリーを調製し、ドクターブレード法により厚さ１００μｍと厚さ１５μｍの第１及び２固体電解質成形体としてのシートを作製した。
【００５０】
次に、燃料極成形体の作製について説明する。平均粒径が０．４μｍのＮｉ粉末に対し、平均粒径が０．４〜０．８μｍの範囲の各粒径を有するＹ₂Ｏ₃を８モル％の割合で含有するＺｒＯ₂粉末を数種類準備し、Ｎｉ／ＹＳＺ比率（重量分率）が５５／４５から７５／２５の範囲になるように数種類調合し、粉砕混合処理を行い、スラリー化した。
【００５１】
その後、調製したスラリーを第２固体電解質成形体上に９〜６５μｍの範囲の厚さで、全面に印刷して燃料極成形体を作製した。従って、第２固体電解質成形体と燃料極成形体の端面は同一面となっている。燃料極を構成するＮｉ／ＹＳＺ混合粉体の各含有比率、各粉体の粒径、また燃料極のシート厚と焼成後の膜厚を表１に示す。
【００５２】
次に、市販の純度９９．９％以上のＬａ₂Ｏ₃、Ｃｒ₂Ｏ₃、ＭｇＯを出発原料として、これをＬａ（Ｍｇ_0.3Ｃｒ_0.7）_0.97Ｏ₃の組成になるように秤量混合した後、１５００℃で３時間仮焼粉砕して、平均粒子径が１〜２μｍの固溶体粉末を得た。この固溶体粉末を用いてスラリーを調製し、ドクターブレード法により厚さ１００μｍの集電体成形体を作製した。
【００５３】
まず、前記空気極仮焼体に前記第１固体電解質仮焼体を、その両端部が開口するようにロール状に巻き付け１１５０℃で５時間の条件で仮焼した。仮焼後、第１固体電解質仮焼体の両端部間を空気極仮焼体を露出させるように平坦に研磨し、連続した同一面を形成するように加工した。
【００５４】
次に、第１固体電解質仮焼体表面に、燃料極成形体が形成された第２固体電解質成形体を、第１固体電解質成形体と第２固体電解質成形体が当接するように積層し、乾燥した後、上記連続同一面に集電体成形体を貼り付け、この後、大気中１５００℃で６時間の条件で共焼結を行い、共焼結体を作製した。
【００５５】
作製した共焼結体の燃料極の評価を行うため、共焼結後の第２固体電解質と燃料極との界面の収縮差、また燃料極の膜剥離の有無を確認した。第２固体電解質と燃料極との界面の収縮差は、セルの長さ方向の固体電解質の端面Ｂと燃料極の端面Ａとの間隔ｘを測定することにより求め、燃料極の膜剥離については目視により観察した。その結果を、表１に示す。
【００５６】
【表１】

【００５７】
表１より、本発明範囲外の試料Ｎｏ．１は、焼成後の収縮差が０．２８ｍｍで他の試料に比べ極めて大きく、界面観察より固体電解質内部へのクラックの進行が認められた。試料Ｎｏ．６は共焼結を行った直後に燃料極全体が固体電解質との界面から剥離した。一方、本発明品である試料においては、いずれも燃料極の剥離も見られず、焼成後の収縮差が０．１３ｍｍ以下で、界面観察においてもクラックの発生は見当たらず良好な界面を形成していた。
【００５８】
実施例２
実施例１で用いた試料Ｎｏ．１、２、３、８、１２の固体電解質型燃料電池セルを作製し、セルの出力密度、実抵抗値、また燃料極サイトの分極値を測定した。その結果を表２に示す。
【００５９】
まず、円筒型セルを作製するため、前記共焼結体片端部に封止部材の接合を行った。封止部材の接合は、以下のような手順で行った。Ｙ₂Ｏ₃を８モル％の割合で含有する平均粒子径が１μｍのＺｒＯ₂粉末に水を溶媒として加えてスラリーを調製し、このスラリーに前記共焼結体の片端部を浸漬し、厚さ１００μｍになるように片端部外周面に塗布し１２０℃の温度で１時間乾燥した。封止部材としてのキャップ形状を有する成形体は、前記スラリー組成と同組成の粉末を用いて静水圧成形（ラバープレス）を行い切削加工した。その後、前記スラリーを被覆した前記共焼結体片端部を封止部材用成形体に挿入し、大気中１３００℃の温度で１時間焼成を行った。
【００６０】
発電は、１０００℃でセルの内側に空気を、外側に水素を流し、出力値が安定した際の初期値と１０００時間保持後の値でそれぞれの性能を測定評価した。
【００６１】
【表２】

【００６２】
燃料極と固体電解質間の界面で焼成収縮差が極めて大きく発生した本発明範囲外の試料Ｎｏ．１は、初期の段階から他の試料に比べ出力密度が低く、実抵抗値と燃料極分極値が高くなっていることが判る。１０００時間経過後においても、更に実抵抗値と燃料極分極値は高くなり、このことから固体電解質内部へのクラックの進展とそれに伴う界面での反応サイトの減少が劣化につながることを確認できた。
【００６３】
焼成収縮差が０．１３ｍｍ以下の本発明の試料においては、いずれも出力密度が初期の段階で０．３４Ｗ／ｃｍ²を上回り、１０００時間経過後も出力密度がほぼ安定しているか若しくは高くなっていく傾向がみられた。また、実抵抗値と燃料極分極値においても、１０００時間経過後も特に大きな変化はみられず安定した値を示した。
【００６４】
実施例３
第１燃料極成形体として、Ｎｉ／ＹＳＺの重量比率が７０／３０、Ｎｉ粒径が０．４μｍ、ＹＳＺ粒子径が０．６μｍ、シート厚を１１μｍとし、この第１燃料極成形体の上面に、表３に示すような組成を有するスラリーを、塗布し、乾燥して第２燃料極成形体を形成する以外は、上記実施例１と同様して固体電解質型燃料電池セルを作製した。
【００６５】
共焼結後の固体電解質と燃料極との界面の収縮差、また膜剥離の有無を確認した。その結果を、表３に示す。
【００６６】
【表３】

【００６７】
この表３から、単に、第１燃料極成形体よりも第２燃料極成形体のＹＳＺ粒子の平均粒径が大きい試料Ｎo.１４〜１７では、第１燃料極成形体のみ形成した試料Ｎo.２よりも焼成収縮差が小さくなることが判る。そして、第１燃料極成形体のＹＳＺ粒子の平均粒径が０．８μｍ以下で、第２燃料極成形体のＹＳＺ粒子の平均粒径が１μｍ以上の場合には、さらに焼成収縮差が小さくなっていることが判る。
【００６８】
【発明の効果】
本発明の固体電解質型燃料電池セルでは、空気極成形体、固体電解質成形体、燃料極成形体を順次積層し、同時焼成したとしても、部材間における焼成収縮差、熱膨張差に伴う応力を緩和できるため、固体電解質からの燃料極の剥離を防止できるとともに、燃料極と固体電解質との焼成収縮差を小さくできる。
【００６９】
このように、燃料極と固体電解質との焼成収縮差を小さくできるため、固体電解質と燃料極の界面から固体電解質内部に生成するクラック（亀裂）を阻止することができ、燃料極と固体電解質間の分極値の増大、また固体電解質成分の実抵抗値の増大を防止でき、これに伴い初期の高い出力密度を長期的に亘って維持できる。
【図面の簡単な説明】
【図１】本発明の円筒状固体電解質型燃料電池セルを示す断面図である。
【図２】本発明の円筒状固体電解質型燃料電池セルを示す斜視図である。
【図３】燃料極と固体電解質の境界近傍を拡大して示す正面図である。
【図４】燃料極成形体が積層された第２固体電解質成形体を、第１固体電解質成形体の表面に巻き付けて積層する状態を示す説明図である。
【図５】燃料極を２層構造とした本発明の円筒状固体電解質型燃料電池セルを示す断面図である。
【図６】従来の円筒状の固体電解質型燃料電池セルを示す斜視図である。
【符号の説明】
３１・・・固体電解質
３２・・・空気極
３３・・・燃料極
３３ａ・・・第１燃料極層
３３ｂ・・・第２燃料極層
５１・・・空気極成形体
５３・・・第１固体電解質成形体
５４・・・燃料極成形体
５５・・・第２固体電解質成形体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid oxide fuel cell in which a solid electrolyte and a fuel electrode are sequentially laminated on the surface of an air electrode.
[0002]
[Prior art]
Conventionally, a solid oxide fuel cell has a high power generation efficiency because its operating temperature is as high as 900 to 1050 ° C., and is expected as a third generation power generation system.
[0003]
Generally, cylindrical and flat plate types are known as solid oxide fuel cells. The flat fuel cell has a feature that the power density per unit volume of power generation is high, but there are problems such as imperfect gas seal and non-uniform temperature distribution in the cell for practical use. On the other hand, the cylindrical fuel cell has the characteristics that although the power density is low, the cell has high mechanical strength and the temperature in the cell can be kept uniform. Both types of solid oxide fuel cells have been actively researched and developed taking advantage of their characteristics.
[0004]
As shown in FIG. 6, a single cell of a cylindrical fuel cell is formed with a porous air electrode support tube 2 made of a LaMnO ₃ material having an open porosity of about 30 to 40%, and Y ₂ O ₃ is formed on the surface thereof. A solid electrolyte 3 made of stabilized ZrO ₂ is coated, and a porous Ni-zirconia fuel electrode 4 is provided on this surface. In the fuel cell module, each single cell is connected via a LaCrO _{3 current} collector (interconnector) 5. Power generation is performed at a temperature of 1000 to 1050 ° C. by flowing air (oxygen) 6 inside the air electrode support tube 2 and flowing fuel (hydrogen) 7 outside.
[0005]
As a method of manufacturing the fuel cell as described above, for example, an insulating powder made of CaO-stabilized ZrO ₂ is formed into a cylindrical shape by an extrusion method or the like, and then fired to produce a cylindrical support. A slurry of an air electrode, a solid electrolyte, a fuel electrode, and a current collector is applied to the outer peripheral surface of the support and sequentially fired and laminated, or electrochemical deposition (EVD method) is applied to the surface of the cylindrical support. ) And plasma spraying methods, etc., an air electrode, a solid electrolyte, a fuel electrode, and a current collector are sequentially formed.
[0006]
In recent years, in order to simplify the cell manufacturing process and reduce the manufacturing cost, a so-called co-sintering method in which at least two of the constituent materials are simultaneously fired has been proposed. In this co-sintering method, for example, a solid electrolyte molded body and a current collector molded body are wound around a cylindrical air electrode molded body in a roll shape and fired simultaneously, and then a fuel electrode layer is formed on the surface of the solid electrolyte layer It is a method to do. In order to simplify the process, a co-sintering method in which a fuel electrode molded body is further laminated on the surface of the solid electrolyte molded body and co-fired has been proposed.
[0007]
This co-sintering method is a very simple process and has a small number of manufacturing steps, and is advantageous in improving the yield during manufacturing of cells and reducing costs. In such a fuel cell by the co-sintering method, a solid electrolyte composed of Y ₂ O ₃ stabilized or partially stabilized ZrO ₂ is used, and the thermal expansion coefficient is matched with this solid electrolyte. A perovskite complex oxide composed of LaMnO ₃ in which part of La is substituted with Y and Ca is used (see JP-A-10-162847, etc.).
[0008]
[Problems to be solved by the invention]
However, when a solid electrolyte molded body and a fuel electrode molded body are laminated on a cylindrical air electrode molded body and a cylindrical fuel cell is produced using a co-sintering method, the fuel electrode itself peels off after sintering. In addition, there is a problem that the power generation performance deteriorates due to the large difference in firing shrinkage between the fuel electrode and the solid electrolyte.
[0009]
That is, in the conventional co-sintering method, the thickness of the fuel electrode has not been optimized. For example, when the thickness of the fuel electrode molded body is large, the problem of the thermal expansion coefficient between the fuel electrode and the solid electrolyte is reduced. There was a problem that the fuel electrode itself was peeled off after sintering without relaxation.
[0010]
Further, when the thickness of the fuel electrode molded body is thin, the end surface in the cell length direction of the fuel electrode molded body is aligned with the end surface in the cell length direction of the solid electrolyte molded body, After the sintering, the end face of the fuel electrode moves greatly inward from the end face of the solid electrolyte, that is, the fuel electrode contracts greatly with respect to the solid electrolyte, and when the interface structure is observed, the interface between the fuel electrode and the solid electrolyte is From the viewpoint of power generation performance, cracks progress from the inside of the solid electrolyte to the inside of the solid electrolyte. As a result, from the viewpoint of power generation performance, as the shrinkage difference increases, the polarization of the fuel electrode site There is a problem that the value and the actual resistance value of the cell constituent component are increased from the initial stage.
[0011]
An object of the present invention is to provide a solid oxide fuel cell that can prevent peeling of the fuel electrode and reduce the difference in firing shrinkage between the fuel electrode and the solid electrolyte to improve the power generation performance.
[0012]
[Means for Solving the Problems]
The solid oxide fuel cell of the present invention is obtained by laminating a first solid electrolyte molded body on an air electrode molded body (which also includes a calcined one) , and the first solid electrolyte molded body (calcined). And the second solid electrolyte molded body on which the fuel electrode molded body is laminated, so that the first solid electrolyte molded body and the second solid electrolyte molded body are in contact with each other, While being simultaneously fired, the thickness of the fuel electrode is 5 to 20 μm.
[0013]
By adopting such a configuration, even if the air electrode molded body, the solid electrolyte molded body, and the fuel electrode molded body are sequentially laminated and fired at the same time, the stress due to the difference in firing shrinkage between the members can be relieved. Therefore, peeling of the fuel electrode from the solid electrolyte can be prevented, and the firing shrinkage difference between the fuel electrode and the solid electrolyte can be reduced.
[0014]
Thus, since the difference in firing shrinkage between the fuel electrode and the solid electrolyte can be reduced, it is possible to prevent cracks generated in the solid electrolyte from the interface between the solid electrolyte and the fuel electrode. As a result, an increase in the polarization value between the fuel electrode and the solid electrolyte and an increase in the actual resistance value of the solid electrolyte component can be prevented, and accordingly, an initial high power density can be maintained over a long period.
[0016]
For example, a laminate of a first solid electrolyte formed body containing ZrO ₂ formed on the surface of an air electrode formed body and a _second solid electrolyte formed body containing ZrO ₂ and a fuel electrode formed body containing metal particles. After laminating the sheet-shaped laminated molded body composed of the first solid electrolyte molded body so that the second solid electrolyte molded body is in contact with the first solid electrolyte molded body, it is fired.
[0017]
Thus, after producing the sheet-like laminated molded body of the second solid electrolyte molded body and the fuel electrode molded body, the second solid electrolyte molded body is brought into contact with the first solid electrolyte molded body. Thus, when fired, the fuel electrode and the solid electrolyte can be firmly joined, and separation of the fuel electrode from the solid electrolyte can be prevented.
[0018]
Furthermore, it is desirable that the difference in firing shrinkage between the fuel electrode and the solid electrolyte is reduced so that the distance between the end face of the solid electrolyte and the end face of the fuel electrode is 0.15 mm or less.
[0019]
The fuel electrode contains metal particles and ZrO ₂ particles, and the fuel electrode includes a first fuel electrode layer on the solid electrolyte side and a second fuel electrode layer formed on the surface of the first fuel electrode layer. becomes, the average particle diameter of the ZrO ₂ grains of the first fuel electrode layer, it is desirable to be smaller than the average particle size of the ZrO ₂ particles of the second fuel electrode layer.
[0020]
This is because the fine ZrO ₂ particles in the first fuel electrode layer sufficiently support the metal particles and suppress the growth of the metal particles in the fuel electrode, and contact between the metal particles in the fuel electrode and the solid electrolyte. The number of points can be increased, the polarization value of the fuel electrode site can be reduced, and the firing shrinkage of the fuel electrode can be reduced by the ZrO ₂ particles having a large average particle diameter of the second fuel electrode layer. The difference in firing shrinkage from the solid electrolyte can be reduced.
[0021]
That is, in the average particle diameter of the metal particles and ZrO ₂ particles constituting the fuel electrode, the smaller the average particle diameter of the ZrO ₂ particles, the easier it is to form a skeleton for suppressing the particle growth of the metal particles. Greatly suppresses growth. On the other hand, the larger the average particle size of the ZrO ₂ particles, the smaller the firing shrinkage of the fuel electrode, and the closer to the solid electrolyte.
[0022]
In particular, it is desirable that the average particle diameter of the ZrO ₂ particles in the first fuel electrode layer is 0.8 μm or less, and the average particle diameter of the ZrO ₂ particles in the second fuel electrode layer is 1 μm or more.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
In the solid electrolyte fuel cell according to the present invention, for example, as shown in FIG. 1, an air electrode 32 is formed on the inner surface of a cylindrical solid electrolyte 31, and a fuel electrode 33 is formed on the outer surface to form a cell body 34. A current collector 35 (interconnector) is electrically connected to 32.
[0024]
That is, a notch 36 is formed in a part of the solid electrolyte 31, and a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 is exposed, and the solid electrolyte near the exposed surface 37 and the notch 36. The surface of 31 is covered with a current collector 35, and the current collector 35 is joined to the surface of both ends of the solid electrolyte 31 and the surface of the air electrode 32 exposed from the notch 36 of the solid electrolyte 31.
A current collector 35 that is electrically connected to the air electrode 32 is formed on the outer surface of the cell body 34 and is formed so as to cover a continuous identical surface 39 having almost no step, and is electrically connected to the fuel electrode 33. It has not been. The current collector 35 is electrically connected to the fuel electrode of another cell via a Ni felt when connecting the cells, thereby forming a fuel cell module. The continuous identical surface 39 is formed by polishing between both ends of the solid electrolyte until both ends of the solid electrolyte and a part of the air electrode become substantially the same continuous surface.
As the solid electrolyte 31, for example, partially stabilized or stabilized ZrO ₂ containing ₃ to 15 mol% of Y ₂ O ₃ is used. Further, as the air electrode 32, for example, LaMnO ₃ in which La is mainly substituted by 10 to 20 atomic% with Ca or Sr is used, and as the current collector 35, for example, Cr is mainly substituted with Mg by 10 to 30 atomic%. LaCrO ₃ is used. As the fuel electrode 33, ZrO ₂ (containing Y ₂ O ₃ ) cermet containing 50 to 80% by weight of Ni is used. The solid electrolyte 31, the air electrode 32, the current collector 35, and the fuel electrode 33 are not limited to the above examples, and known materials may be used.
In the solid electrolyte fuel cell of the present invention, the solid electrolyte 31 includes a first solid electrolyte 31a formed on the surface of the air electrode 32 and a second solid electrolyte 31b formed on the surface of the first solid electrolyte 31a. The fuel electrode 33 is formed on the surface of the second solid electrolyte 31b, and the thickness of the fuel electrode 33 is 5 to 20 μm.
[0025]
The thickness of the fuel electrode 33 is set to 5 to 20 μm because if the thickness of the fuel electrode 33 is smaller than 5 μm, the shrinkage during firing increases with the growth of Ni particles, while if the thickness is larger than 20 μm, This is because after the sintering, the fuel electrode 33 itself peels off without being able to alleviate the problem of the coefficient of thermal expansion between the fuel electrode 33 and the solid electrolyte 31. The thickness of the fuel electrode 33 is desirably 10 to 20 μm from the viewpoint of reducing the contraction amount of the fuel electrode 33 and preventing the fuel electrode 33 from peeling off.
[0026]
In the fuel electrode 33, the average particle diameter of ZrO ₂ particles is 0.4 to 0.8 μm, and the average particle diameter of Ni particles is 0.2 to 0.6 μm. When the average particle size of the ZrO ₂ particles is smaller than 0.4 μm, a difference in firing shrinkage from the solid electrolyte tends to occur remarkably, and when the average particle size of the Ni particles is larger than 0.6 μm This is because there is a tendency that the contact point between the Ni and ZrO ₂ particles cannot be increased. Further, when the average particle size of Ni particles is smaller than 0.2 μm, uniform mixing with ZrO ₂ particles is difficult, and conversely, there is a tendency to aggregate, and the average particle size of ZrO ₂ particles is 0.8 μm. If it is larger than the range, uniform support around the Ni particles tends to be impossible.
[0027]
FIG. 2 is a perspective view of the solid oxide fuel cell of the present invention, and FIG. 3 is an enlarged front view showing the vicinity of the boundary between the fuel electrode 33 and the solid electrolyte 31. As shown in FIG. 3, in the solid oxide fuel cell of the present invention, the end surface A of the fuel electrode 33 in the cell length direction and the end surface B of the solid electrolyte 31 formed on the lower surface thereof in the cell length direction The interval x is set to 0.15 mm or less. When the distance x between the end face A and the end face B is larger than 0.15 mm, the firing shrinkage difference between the fuel electrode 33 and the solid electrolyte 31 (first solid electrolyte 31a) is large, and cracks tend to be generated in the solid electrolyte 31. Because there is. The distance x between the end surface A and the end surface B is preferably 0.10 mm or less from the viewpoint of preventing crack formation in the solid electrolyte 31.
[0028]
In the solid oxide fuel cell of the present invention, first, a cylindrical air electrode molded body is formed. This cylindrical air electrode molded body is prepared, for example, by weighing and mixing raw materials of La ₂ O ₃ , Y ₂ O ₃ , CaO, and MnO ₂ in accordance with a predetermined composition, and at a temperature of about 1500 ° C. for 2 to 10 hours. Calcination is performed, and then pulverized to a particle size of 4 to 8 μm.
[0029]
The prepared powder is mixed and kneaded with a binder to produce a cylindrical air electrode molded body by extrusion molding. Further, the binder is debindered and calcined at 1200 to 1250 ° C. A fired body is produced.
[0030]
As a sheet-like first solid electrolyte molded body, a slurry obtained by adding toluene, a binder, and a commercially available dispersant to a predetermined powder and molding it into a thickness of, for example, 100 to 120 μm by a method such as a doctor blade is used. The first solid electrolyte molded body is pasted and calcined on the surface of the cylindrical air electrode calcined body.
[0031]
Next, a sheet-shaped fuel electrode molded body is produced. First, for example, a slurry prepared by adding toluene and a binder to NiO / YSZ mixed powder prepared at a predetermined ratio is prepared. Similarly to the production of the first solid electrolyte molded body, the molded and dried mold is formed to form a sheet-like second solid electrolyte molded body having a thickness of 15 μm, for example.
[0032]
After the fuel electrode layer molded body was printed and dried on the second solid electrolyte molded body, the fuel electrode layer molded body 54 was formed on the first solid electrolyte calcined body 53 as shown in FIG. The two solid electrolyte molded body 55 is wound and laminated so that the second solid electrolyte molded body 55 contacts the first solid electrolyte calcined body 53. Reference numeral 51 denotes an air electrode calcined body.
[0033]
The thickness of the fuel electrode layer molded body is 9 to 60 μm. When the thickness of the fuel electrode layer compact is less than 9 μm, the firing shrinkage difference is promoted as the Ni grains grow. On the other hand, when the thickness is greater than 60 μm, the fuel electrode has a thermal expansion coefficient mismatch with the solid electrolyte. It becomes easy to peel. From this point, the thickness of the fuel electrode molded body is particularly preferably 25 to 40 μm.
[0034]
The Ni / YSZ mixed powder constituting the fuel electrode layer molded body is a raw material powder having an average particle diameter of Ni powder of 0.2 to 0.6 μm and an average particle diameter of YSZ powder of 0.4 to 0.8 μm. In order to increase the dispersibility after blending to a predetermined ratio, wet pulverization mixing is performed using ZrO ₂ balls. When the particle diameter of the YSZ powder constituting the fuel electrode is larger than 0.8 μm, there is no problem in terms of firing shrinkage difference, but Ni particles are locally supported because Ni particles are not sufficiently supported at the micro level.
[0035]
Furthermore, the firing shrinkage difference can be reduced also in the combination of the particle sizes of Ni powder and YSZ powder constituting the fuel electrode. When the YSZ powder has a particle size of 0.8 μm or more, there is no problem in terms of the difference in shrinkage at the time of firing, but Ni particle grain growth cannot be suppressed, and as a result, the polarization of the fuel electrode site due to the decrease in the number of reaction sites The output performance decreases with the increase.
[0036]
As a result, the number of contacts between Ni / YSZ decreases from the viewpoint of the number of reaction sites, and therefore the polarization value of the fuel electrode site increases extremely and the output performance decreases. On the other hand, when the Ni content ratio is higher than 80%, the thermal expansion coefficient is inconsistent with the solid electrolyte membrane, and peeling is likely to occur.
[0037]
Next, as in the preparation of the solid electrolyte molded body, the current collector molded body molded to a thickness of 100 to 120 μm is attached to a predetermined location.
[0038]
Thereafter, the laminated body of the cylindrical air electrode molded body 51, the solid electrolyte molded

bodies

53 and 55, the fuel electrode molded body 54, and the current collector molded body is simultaneously co-fired at a temperature of 1400 to 1550 ° C. in the atmosphere. Is done.
[0039]
In the solid oxide fuel cell configured as described above, even if the air electrode molded body, the solid electrolyte molded body, and the fuel electrode molded body are sequentially laminated and fired at the same time, the amount of firing shrinkage generated between the members, the heat Since the reaction associated with the expansion difference can be mitigated, the fuel electrode can be prevented from peeling from the solid electrolyte, and the difference in firing shrinkage between the fuel electrode and the solid electrolyte can be reduced, thereby preventing cracks generated inside the solid electrolyte. As a result, an increase in the polarization value between the fuel electrode and the solid electrolyte and an increase in the actual resistance value of the solid electrolyte component can be prevented, and an initial high power density can be maintained over a long period of time.
[0040]
In addition, instead of winding and laminating the fuel electrode molded body around the surface of the solid electrolyte molded body, a sheet-shaped laminated molded body of the second solid electrolyte molded body and the fuel electrode molded body is produced. Are laminated so that the second solid electrolyte molded body comes into contact with the first solid electrolyte molded body, so that the fuel electrode and the solid electrolyte can be firmly joined, and the fuel electrode can be prevented from being peeled off from the solid electrolyte.
[0041]
FIG. 5 shows another solid oxide fuel cell of the present invention. In this example, the fuel electrode 33 includes a first fuel electrode layer 33a on the solid electrolyte side and a second fuel electrode on the outer surface side. The average particle diameter of the ZrO ₂ particles of the first fuel electrode layer 33a is smaller than the average particle diameter of the ZrO ₂ particles of the second fuel electrode layer 33b. Here, the average particle size of ZrO ₂ grains of the first fuel electrode layer 33a is a 0.8μm or less, an average particle diameter of the ZrO ₂ particles of the second fuel electrode layer 33b is equal to or greater than 1 [mu] m, other configurations the Same as example.
[0042]
Here, the average particle diameter of the ZrO ₂ particles of the first fuel electrode layer 33a is set to 0.8 μm or less because the fine ZrO ₂ particles of the first fuel electrode layer are sufficiently around the metal particles (Ni). This is because it is possible to suppress the grain growth of the metal particles of the fuel electrode and increase the number of contact points between the metal particles of the fuel electrode 33 and the solid electrolyte 31.
[0043]
The reason why the average particle diameter of the ZrO ₂ particles in the second fuel electrode layer 33b is 1 μm or more is that the firing shrinkage of the fuel electrode 33 is reduced by the ZrO ₂ particles having a large average particle diameter in the second fuel electrode layer 33b. This is because the difference in firing shrinkage between the fuel electrode 33 and the solid electrolyte 31 can be reduced. Although the metal particles of the fuel electrode grow at the firing temperature, the ZrO ₂ particles hardly grow.
[0044]
In such a solid oxide fuel cell, the first fuel electrode layer molded body is printed on the surface of the second solid electrolyte molded body and dried, and then the second fuel electrode layer molded body is formed on the first fuel electrode layer molded body. Can be produced in the same manner as described above except that the laminated molded body is laminated on the surface of the first solid electrolyte calcined body.
[0045]
In the above example, the cylindrical solid electrolyte fuel cell has been described. However, a flat plate fuel cell may be used.
[0046]
In the above example, the air electrode molded body and the first solid electrolyte molded body are temporarily calcined, and the second solid electrolyte molded body and the fuel electrode molded body are formed on the air electrode molded body. A first solid electrolyte molded body, a second solid electrolyte molded body, and a fuel electrode molded body may be formed on the body.
[0047]
【Example】
Example 1
In order to produce a cylindrical solid electrolyte fuel cell by a co-sintering method, a cylindrical air electrode molded body was first produced by the following procedure.
[0048]
Using commercially available La ₂ O ₃ , Y ₂ O ₃ , CaCO ₃ , Mn ₂ O ₃ with a purity of 99.9% or more as a starting material, weighed to a composition of La _0.56 Y _0.14 Ca _0.3 MnO _3. An organic binder was added, extrusion molding was performed, and an air electrode calcined body was formed by removal and calcining.
[0049]
Next, a slurry was prepared using a ZrO ₂ powder having an average particle diameter of 1 to ₂ μm containing Y ₂ O ₃ at a ratio of 8 mol%, and the first and the first 100 μm and 15 μm thick first and A sheet as a two-solid electrolyte molded body was produced.
[0050]
Next, production of the fuel electrode molded body will be described. Several kinds of ZrO ₂ powders containing 8 mol% of Y ₂ O ₃ having each particle diameter in the range of 0.4 to 0.8 μm with respect to Ni powder having an average particle diameter of 0.4 μm Prepared, prepared several kinds of Ni / YSZ ratio (weight fraction) in the range of 55/45 to 75/25, pulverized and mixed, and slurried.
[0051]
Thereafter, the prepared slurry was printed on the entire surface of the second solid electrolyte molded body with a thickness in the range of 9 to 65 μm to produce a fuel electrode molded body. Therefore, the end surfaces of the second solid electrolyte molded body and the fuel electrode molded body are the same surface. Table 1 shows the content ratios of the Ni / YSZ mixed powder constituting the fuel electrode, the particle diameter of each powder, the sheet thickness of the fuel electrode, and the film thickness after firing.
[0052]
Next, after commercially available La ₂ O ₃ , Cr ₂ O ₃ and MgO having a purity of 99.9% or more are used as starting materials, they are weighed and mixed so as to have a composition of La (Mg _0.3 Cr _0.7 ) _0.97 O _3. By calcining and pulverizing at 1500 ° C. for 3 hours, a solid solution powder having an average particle size of 1 to 2 μm was obtained. A slurry was prepared using this solid solution powder, and a current collector molded body having a thickness of 100 μm was prepared by a doctor blade method.
[0053]
First, the first solid electrolyte calcined body was wound around the air electrode calcined body in a roll shape so that both ends thereof were open, and calcined at 1150 ° C. for 5 hours. After the calcination, the first solid electrolyte calcined body was polished flat so as to expose the air electrode calcined body and processed so as to form a continuous same surface.
[0054]
Next, the second solid electrolyte molded body on which the fuel electrode molded body is formed is laminated on the surface of the first solid electrolyte calcined body so that the first solid electrolyte molded body and the second solid electrolyte molded body are in contact with each other, After drying, the current collector molded body was attached to the continuous same surface, and then co-sintered at 1500 ° C. in the atmosphere for 6 hours to produce a co-sintered body.
[0055]
In order to evaluate the fuel electrode of the produced co-sintered body, the shrinkage difference at the interface between the second solid electrolyte and the fuel electrode after co-sintering and the presence or absence of film peeling of the fuel electrode were confirmed. The difference in shrinkage at the interface between the second solid electrolyte and the fuel electrode is obtained by measuring the distance x between the end surface B of the solid electrolyte and the end surface A of the fuel electrode in the cell length direction. It was observed visually. The results are shown in Table 1.
[0056]
[Table 1]

[0057]
From Table 1, sample no. In No. 1, the shrinkage difference after firing was 0.28 mm, which was extremely large compared to other samples, and the progress of cracks in the solid electrolyte was observed from the interface observation. Sample No. 6 immediately after co-sintering, the entire fuel electrode was peeled off from the interface with the solid electrolyte. On the other hand, in the samples according to the present invention, none of the fuel electrode was peeled off, the shrinkage difference after firing was 0.13 mm or less, and no crack was found in the interface observation, and a good interface was formed. It was.
[0058]
Example 2
Sample No. used in Example 1 1, 2, 3, 8, and 12 solid oxide fuel cells were fabricated, and the output density, actual resistance value, and polarization value of the fuel electrode site were measured. The results are shown in Table 2.
[0059]
First, in order to produce a cylindrical cell, a sealing member was joined to one end of the co-sintered body. The sealing member was joined by the following procedure. A slurry is prepared by adding water as a solvent to a ZrO ₂ powder containing Y ₂ O ₃ at a ratio of 8 mol% and having an average particle diameter of 1 μm, and one end of the co-sintered body is immersed in this slurry, The film was applied to the outer peripheral surface of one end so as to have a thickness of 100 μm and dried at a temperature of 120 ° C. for 1 hour. The molded body having a cap shape as a sealing member was subjected to isostatic pressing (rubber press) using a powder having the same composition as the slurry composition and cut. Thereafter, the end portion of the co-sintered body coated with the slurry was inserted into a molded body for a sealing member, and baked at a temperature of 1300 ° C. in the atmosphere for 1 hour.
[0060]
For power generation, air was flown inside the cell and hydrogen was flown outside at 1000 ° C., and the performance was measured and evaluated with the initial value when the output value was stabilized and the value after holding for 1000 hours.
[0061]
[Table 2]

[0062]
Sample Nos. Outside the scope of the present invention, in which the firing shrinkage difference was extremely large at the interface between the fuel electrode and the solid electrolyte. No. 1 shows that the output density is lower than the other samples from the initial stage, and the actual resistance value and the fuel electrode polarization value are high. Even after 1000 hours, the actual resistance value and the fuel electrode polarization value further increased, and from this, it was confirmed that the progress of cracks inside the solid electrolyte and the accompanying decrease in reaction sites at the interface led to deterioration. .
[0063]
In the samples of the present invention having a firing shrinkage difference of 0.13 mm or less, the output density exceeded 0.34 W / cm ² at the initial stage, and the output density was almost stable or increased after 1000 hours. There was a tendency to go. Also, the actual resistance value and the fuel electrode polarization value showed stable values with no significant change even after 1000 hours.
[0064]
Example 3
As the first fuel electrode molded body, the Ni / YSZ weight ratio is 70/30, the Ni particle diameter is 0.4 μm, the YSZ particle diameter is 0.6 μm, and the sheet thickness is 11 μm. A solid oxide fuel cell was produced in the same manner as in Example 1 except that a slurry having the composition shown in Table 3 was applied and dried to form a second fuel electrode molded body.
[0065]
The shrinkage difference at the interface between the solid electrolyte and the fuel electrode after co-sintering, and the presence or absence of film peeling were confirmed. The results are shown in Table 3.
[0066]
[Table 3]

[0067]
From Table 3, sample Nos. 14 to 17 in which the average particle diameter of the YSZ particles of the second fuel electrode molded body is larger than that of the first fuel electrode molded body, the sample No. 14 formed only with the first fuel electrode molded body. It can be seen that the difference in firing shrinkage is smaller than 2. When the average particle diameter of the YSZ particles of the first fuel electrode molded body is 0.8 μm or less and the average particle diameter of the YSZ particles of the second fuel electrode molded body is 1 μm or more, the firing shrinkage difference is further reduced. You can see that
[0068]
【The invention's effect】
In the solid oxide fuel cell of the present invention, even if the air electrode molded body, the solid electrolyte molded body, and the fuel electrode molded body are sequentially laminated and fired at the same time, the stress due to the firing shrinkage difference and the thermal expansion difference between the members is reduced. Since it can be mitigated, peeling of the fuel electrode from the solid electrolyte can be prevented, and the difference in firing shrinkage between the fuel electrode and the solid electrolyte can be reduced.
[0069]
As described above, since the difference in firing shrinkage between the fuel electrode and the solid electrolyte can be reduced, cracks generated inside the solid electrolyte from the interface between the solid electrolyte and the fuel electrode can be prevented, and the gap between the fuel electrode and the solid electrolyte can be prevented. The increase in the polarization value and the increase in the actual resistance value of the solid electrolyte component can be prevented, and accordingly, the initial high power density can be maintained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a cylindrical solid oxide fuel cell according to the present invention.
FIG. 2 is a perspective view showing a cylindrical solid oxide fuel cell according to the present invention.
FIG. 3 is an enlarged front view showing the vicinity of a boundary between a fuel electrode and a solid electrolyte.
FIG. 4 is an explanatory view showing a state in which a second solid electrolyte molded body on which a fuel electrode molded body is laminated is wound around the surface of the first solid electrolyte molded body and laminated.
FIG. 5 is a cross-sectional view showing a cylindrical solid electrolyte fuel cell of the present invention having a fuel electrode having a two-layer structure.
FIG. 6 is a perspective view showing a conventional cylindrical solid oxide fuel cell.
[Explanation of symbols]
31 ... Solid electrolyte 32 ... Air electrode 33 ... Fuel electrode 33a ... First fuel electrode layer 33b ... Second fuel electrode layer 51 ... Air electrode molded body 53 ... First Solid electrolyte molded body 54 ... Fuel electrode molded body 55 ... Second solid electrolyte molded body

Claims

The first solid electrolyte molded body is laminated on the air electrode molded body, and the second solid electrolyte molded body in which the fuel electrode molded body is laminated on the first solid electrolyte molded body is the first solid electrolyte molded body. The solid electrolyte fuel cell, wherein the second solid electrolyte molded body is laminated so as to be in contact with each other and fired simultaneously, and the thickness of the fuel electrode is 5 to 20 μm.

The solid oxide fuel cell according to claim 1, wherein the distance between the end face and the end face of the fuel electrode of the solid electrolyte is 0.15mm or less.

The fuel electrode contains metal particles and ZrO ₂ particles, and the fuel electrode includes a first fuel electrode layer on the solid electrolyte side and a second fuel electrode layer formed on the surface of the first fuel electrode layer. 3. The solid oxide fuel according to claim 1, wherein an average particle diameter of ZrO ₂ particles in the first fuel electrode layer is smaller than an average particle diameter of ZrO ₂ particles in the second fuel electrode layer. Battery cell.

The average particle size of ZrO ₂ particles of the first fuel electrode layer is not more 0.8μm or less, according to claim 3, wherein the solid having an average particle diameter of the ZrO ₂ particles of the second fuel electrode layer is equal to or is 1μm or more Electrolytic fuel cell.