【０００１】
【発明の属する技術分野】
この発明は、絶縁基体管の外周に多孔質内側電極、緻密電解質、多孔質外側電極を順次積層して構成された４層構造の円筒型高温水蒸気電解セルの改良に関する。
【０００２】
【従来の技術】
高温水蒸気電解セルは水蒸気を電解して水素と酸素を製造する装置で、通常１０００℃程度の高温で運転されるが、このうち円筒型高温水蒸気電解セルには従来円筒状の絶縁基体管の外周に多孔質内側電極、緻密電解質、多孔質外側電極を順次積層して構成された４層構造のものと、基体管を設けない３層構造のものがあるが、４層構造のものは３層構造のものと比べて電解質内に内側電極と外側電極を接続するインターコネクタ部の形成が容易であるという特徴がある。
【０００３】
４層構造の円筒型高温水蒸気電解セルは絶縁基体管の外周上に内側電極、電解質、外側電極を燒結、溶射、ＥＶＤ法などにより順次成膜して製造される。
【０００４】
この場合、電極材料としては熱膨張率１．２ ×１０−５程度のＮｉ−ＹＳＺ（ イットリア安定化ジルコニア）、ＬａＳｒＭｎＯ３ 系の材料が使用され、電解質材料としては熱膨張率１．０３×１０−５程度のＹＳＺ が使用され、基体管材料としては従来より電解質と同程度の熱膨張率を有するＣＳＺ （ＣａＯ 安定化ジルコニア：熱膨張率９．１ 〜１０×１０−６）が用いられている。
【０００５】
【発明が解決しようとする課題】
しかし、このセルの各層の厚みは基本管が２ｍｍ 程度、電解質、電極が０．１ｍｍ 程度であるが、一般に成膜温度が１０００℃以上と高く、またその運転も１０００℃程度で行われるため、室温状態では電解セルの各層の劣化、破損につながる応力が働く虞がある。
【０００６】
そこで、本願発明者等は４層構造の円筒型高温水蒸気電解セルについて円周方向の残留応力について検討を行った結果、図２のような解析結果を得た。
【０００７】
これによれば、内側電極層と外側電極層に２００ＭＰａ以上の引っ張り応力が働き、電解質層には１５０ＭＰａ程度の圧縮応力が働くことが明らかとなった。
【０００８】
この場合、ＹＳＺ 等で構成される電解質層に１５０ＭＰａ以上の圧縮応力が働いても、電解質層が劣化、破損されることがないが、２００ＭＰａ以上の引っ張り応力はＮｉ−ＹＳＺ、Ｌａ１−ｘＳｒｘＭｎＯ３ 系の電極材料の引っ張り強度を大きく越えており、この応力の低減が重大な課題である。
【０００９】
【課題を解決するための手段】
この発明は、上記実情に鑑み、絶縁基体管の外周に多孔質内側電極、緻密電解質、多孔質外側電極の各層を順次積層して構成され、且つ前記内側電極材質乃至前記外側電極材質の熱膨張率が前記電解質のそれに比べて大きな円筒型高温水蒸気電解セルにおいて、前記絶縁基体管をＭｇＯ、ＭｇＡｌ ２ Ｏ ４ 混合物焼結体を用いて構成し、且つその熱膨張率を前記内側電極材質又は前記外側電極材質の熱膨張率のうち大きな方と一致若しくはこれより少し大きめにしたことを特徴とする円筒型高温水蒸気電解セルを提案するものである。
【００１０】
【作用】
上記構成の電解セルにおいて基体管の熱膨張率を電極材質の熱膨張率と同程度とすることにより、電極に働く引っ張り残留応力を２０ＭＰａ 以下に低減でき、この結果引っ張り残留応力による電極の劣化、破損を免れることができる。
【００１１】
一方、電解質には引っ張り残留応力は発生せず、６００ＭＰａ以上の圧縮残留応力が働くが、ＹＳＺ 等の電解質材質ではこの圧縮残留応力により電解質が破損されることはない。
【００１２】
この発明においては電極材質としては混合比Ｎｉ４０〜５０％，ＹＳＺ６０ 〜５０％ のＮｉ−ＹＳＺ混合物、Ｌａ１−ｘＳｒｘＭｎＯ３（ｘ＝０．１ 〜０．３）系材質、電解質としてはＹＳＺ 、インターコネクタ部にはＬａ１−ｘＳｒｘＣｒＯ３（ｘ＝０．１５ 程度）が使用され、この中基体管の外周にはスラリーコート法、溶射法等で内側電極が成膜され、その外側には電解質がＥＶＤ法、溶射法で緻密に成膜され、インターコネクタ部にはＰＶＤ法で成膜され、成膜され、その外側には外側電極をスラリーコート、溶射法等で成膜する。
【００１３】
なお、熱膨張率において内側電極と外側電極と違いがある場合には、基体管の熱膨張率をこのうち大きな熱膨張率の方に合わせるようにする。
【００１４】
また、電極の熱膨張率と基体管の熱膨張率とを一致させるのが難しい場合には
、基体管の熱膨張率の方が電極のそれよりも多少大きくなるように調整する。
【００１５】
なお、この発明において基体管の熱膨張率を電極材質の熱膨張率と同程度とする手段として、基体管をＭｇＯ，ＭｇＡｌ２Ｏ４ 混合物を用いて構成し、ＭｇＯ とＭｇＡｌ２Ｏ４ の混合比を調節することにより基体管の熱膨張率を電極材質の熱膨張率と同程度にすることができる。
【００１６】
ＭｇＯ，ＭｇＡｌ２Ｏ４ 混合物の混合比を重量比ＭｇＯ：Ａｌ２Ｏ３＝１００：０ 〜０：１００ の範囲内では基体管の熱膨張率を１．３ ×１０−５〜０．８ ×１０−５の範囲に調整でき、好ましくは重量比ＭｇＯ：Ａｌ２Ｏ３ ＝６５：３５ 〜８３：１７ の範囲内で調整することによって、基体管の熱膨張率を１．１ ×１０−５〜１．２ ×１０−５の範囲内で調整できる。
【００１７】
なお、下地の保護の観点から外側に行くほど成膜温度を低くすることが望ましいが、この場合でもこの発明では成膜温度をセルの運転温度より高くすることで
、運転時も室温時も電極、基体管に働く引っ張り残留応力を１０ＭＰａ 以下にすることができ、一方電解質、インターコネクタ部に圧縮残留応力しか発生させないようにすることができる。
【００１８】
また、このような成膜温度を採ることにより運転時の応力の大きさは何れも室温時より大幅に小さくなり、電池の劣化、破損を防止することができる。
【００１９】
【発明の実施の形態】
本発明に係る円筒型高温水蒸気電解セルを実施例に基づいて図面を参照して説明する。以下、電極としてＮｉ−ＹＳＺ，Ｌａ１−ｘＳｒｘＭｎＯ３（ｘ＝０．１ 程度）、電解質としてＹＳＺ 、基体管としてＭｇＯ，ＭｇＡｌ２Ｏ４ スピネル混合物を用いて円筒型高温水蒸気電解セルを製造した実施例について以下に述べる。
【００２０】
ＭｇＯ，ＭｇＡｌ２Ｏ４ スピネルの混合物を気孔率３０ｍｍ， 厚み２ｍｍ，内径１０〜２０ｍｍ程度の円筒に燒結させて基体管を製作する。
【００２１】
この場合、セル製作時の温度又は運転時の温度のうち高い方の温度と室温との間の電極材の熱膨張率を測定し、ＭｇＯ，ＭｇＡｌ２Ｏ４ の混合物燒結体の熱膨張率が測定した電極材の熱膨張率のうち熱膨張率の大きい方と一致若しくはこれより少し大きめになるように、ＭｇＯ とＭｇＡｌ２Ｏ４ スピネルとの混合比を調節する。
【００２２】
この実施例ではセル運転時の温度が約１０００℃であるのに対してセル製作時の最高温度が１３００〜１４００℃であるので、１４００℃と室温との間の電極材の熱膨張率を測定した結果、Ｎｉ−ＹＳＺ燃料極、Ｌａ１−ｘＳｒｘＭｎＯ３空気極の熱膨張率は何れも１．２ ×１０−５であった。そこで、基体管はＭｇＯ とＭｇＡｌ２Ｏ４ スピネルの混合比が重量比でＭｇＯ： Ａｌ２Ｏ３ ＝８３：１７となるように調節した後、内径１２ｍｍ、厚み２ｍｍ 程度で熱膨張率１．２ ×１０−５のパイプ形状のものを製作した。
【００２３】
この基体管外側にＮｉ−ＹＳＺ燃料極或はＬａ１−ｘＳｒｘＭｎＯ３（ｘ＝０．１程度）空気極を１００μｍ 〜５００ μｍ 程度スラリーコートにより作成し、その後ＥＶＤ法によりＹＳＺ 緻密電解質膜を形成し、最後に残りの電極を作成して単電池セルとした。各層の作成条件、作成した厚みを下記表１に示す。
【００２４】
【表１】
【００２５】
次に作成した単セルについて円周方向の残留応力を測定した結果を図１に示す
。
【００２６】
これによれば、Ｎｉ−ＹＳＺ燃料極或はＬａ１−ｘＳｒｘＭｎＯ３（ｘ＝０．１程度）空気極及び外側電極に働く引っ張り残留応力は２０ＭＰａ 以下となり、これによって電極が劣化、破損されることはない。
【００２７】
また、電解質層には引っ張り残留応力は発生せず、６００ＭＰａ以上の圧縮残留応力が働くが、この圧縮残留応力よって電解質層が破損されることはない。
【００２８】
【発明の効果】
以上要するに、この発明によれば４層構造の円筒型高温水蒸気電解セルにおいて電極層に働く引っ張り残留応力を従来の１／１０以下に低減でき、したがって温度昇降過程で頻繁に発生する固体電解質燃料電池の劣化、破損を防止できる。
【図面の簡単な説明】
【図１】この発明に係る円筒型高温水蒸気電解セルにおける円周方向の残留応力を示す図である。
【図２】従来の４層構造の円筒型高温水蒸気電解セルにおける円周方向の残留応力を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement of a cylindrical high-temperature steam electrolysis cell having a four-layer structure in which a porous inner electrode, a dense electrolyte, and a porous outer electrode are sequentially laminated on the outer periphery of an insulating substrate tube.
[0002]
[Prior art]
A high-temperature steam electrolysis cell is a device that produces hydrogen and oxygen by electrolyzing water vapor, and is usually operated at a high temperature of about 1000 ° C. Among them, a cylindrical high-temperature steam electrolysis cell has a conventional cylindrical outer insulating tube. There is a four-layer structure in which a porous inner electrode, a dense electrolyte, and a porous outer electrode are sequentially laminated, and a three-layer structure without a base tube. It is characterized in that it is easier to form an interconnector part for connecting an inner electrode and an outer electrode in an electrolyte than a structure.
[0003]
A four-layer cylindrical high-temperature steam electrolysis cell is manufactured by sequentially forming an inner electrode, an electrolyte, and an outer electrode on the outer periphery of an insulating base tube by sintering, thermal spraying, an EVD method, or the like.
[0004]
In this case, Ni-YSZ (yttria-stabilized zirconia) or LaSrMnO 3 material having a thermal expansion coefficient of about 1.2 × 10 −5 is used as an electrode material, and a thermal expansion coefficient of 1.03 × 10 5 is used as an electrolyte material. -5 of YSZ is used, and CSZ (CaO-stabilized zirconia: coefficient of thermal expansion of 9.1 to 10 × 10 −6 ) having a coefficient of thermal expansion similar to that of an electrolyte is conventionally used as a base tube material. I have.
[0005]
[Problems to be solved by the invention]
However, the thickness of each layer of this cell is about 2 mm for the basic tube and about 0.1 mm for the electrolyte and the electrodes. However, since the film formation temperature is generally as high as 1000 ° C. or more and the operation is performed at about 1000 ° C., In a room temperature state, there is a possibility that a stress which causes deterioration and breakage of each layer of the electrolytic cell may act.
[0006]
The inventors of the present application have studied the residual stress in the circumferential direction of the cylindrical high-temperature steam electrolysis cell having a four-layer structure, and have obtained an analysis result as shown in FIG.
[0007]
According to this, it became clear that a tensile stress of 200 MPa or more acts on the inner electrode layer and the outer electrode layer, and a compressive stress of about 150 MPa acts on the electrolyte layer.
[0008]
In this case, even if a compressive stress of 150 MPa or more acts on the electrolyte layer composed of YSZ or the like, the electrolyte layer is not deteriorated or damaged, but the tensile stress of 200 MPa or more is reduced by Ni-YSZ or La 1-x Sr. the tensile strength of the x MnO 3 system electrode material is significantly beyond the reduction of the stress is a significant challenge.
[0009]
[Means for Solving the Problems]
In view of the above circumstances, the present invention is configured by sequentially laminating each layer of a porous inner electrode, a dense electrolyte, and a porous outer electrode on the outer periphery of an insulating base tube, and further includes a thermal expansion of the inner electrode material to the outer electrode material. in large cylindrical high-temperature steam electrolysis cell than that rate is the electrolyte, the MgO insulating substrate tube, constructed using MgAl 2 O 4 mixture sintered body, and the thermal expansion rate of its said inner electrode material or The present invention proposes a cylindrical high-temperature steam electrolysis cell characterized in that the thermal expansion coefficient of the outer electrode material matches or is slightly larger than the larger one.
[0010]
[Action]
By making the coefficient of thermal expansion of the base tube approximately equal to the coefficient of thermal expansion of the electrode material in the electrolytic cell having the above configuration, the tensile residual stress acting on the electrode can be reduced to 20 MPa or less. As a result, deterioration of the electrode due to the residual tensile stress, Damage can be avoided.
[0011]
On the other hand, no tensile residual stress is generated in the electrolyte, and a compressive residual stress of 600 MPa or more acts. However, in the case of an electrolyte material such as YSZ, the electrolyte is not damaged by the compressive residual stress.
[0012]
The mixing ratio Ni40～50% as electrode material in this invention, YSZ60 ~50% of Ni-YSZ mixture, La 1-x Sr x MnO 3 (x = 0.1 ~0.3) based material, as the electrolyte YSZ, La 1-x Sr x CrO 3 (x = 0.15) is used for the interconnector portion, and an inner electrode is formed on the outer periphery of the base tube by a slurry coating method, a thermal spraying method, or the like. An electrolyte is densely formed on the outside by an EVD method or a spraying method, and a film is formed on the interconnector by a PVD method, and the outside electrode is formed on the outside by a slurry coating method, a spraying method, or the like. I do.
[0013]
When there is a difference in the coefficient of thermal expansion between the inner electrode and the outer electrode, the coefficient of thermal expansion of the base tube is adjusted to the larger coefficient of thermal expansion.
[0014]
If it is difficult to make the coefficient of thermal expansion of the electrode and the coefficient of thermal expansion of the base tube equal, it is adjusted so that the coefficient of thermal expansion of the base tube is slightly larger than that of the electrode.
[0015]
Incidentally, as a means for the thermal expansion coefficient comparable to electrode material the thermal expansion coefficient of the substrate tube in the present invention, the substrate tube configured using MgO, the MgAl 2 O 4 mixture, mixing of MgO and MgAl 2 O 4 By adjusting the ratio, the coefficient of thermal expansion of the base tube can be made similar to the coefficient of thermal expansion of the electrode material.
[0016]
When the mixing ratio of the mixture of MgO and MgAl 2 O 4 is within the range of MgO: Al 2 O 3 = 100: 0 to 0: 100, the coefficient of thermal expansion of the base tube is 1.3 × 10 −5 to 0.8 ×. The coefficient of thermal expansion of the base tube can be adjusted to 1.1 × 10 −5 by adjusting the weight ratio within the range of 10 −5 , preferably within the range of MgO: Al 2 O 3 = 65: 35 to 83:17. It can be adjusted within the range of 1.2 × 10 −5 .
[0017]
In addition, from the viewpoint of protection of the underlayer, it is desirable to lower the film forming temperature as it goes outward, but in this case also, in the present invention, the film forming temperature is set higher than the operating temperature of the cell, so that the electrode can be operated both at room temperature and at room temperature. In addition, the tensile residual stress acting on the base tube can be reduced to 10 MPa or less, while only the compressive residual stress can be generated in the electrolyte and the interconnector.
[0018]
In addition, by adopting such a film forming temperature, the magnitude of the stress during operation becomes significantly smaller than that at room temperature, and the deterioration and breakage of the battery can be prevented.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
A cylindrical high-temperature steam electrolysis cell according to the present invention will be described with reference to the drawings based on an embodiment. Hereinafter, Ni-YSZ, La 1- x Sr x MnO 3 (x = 0.1) as an electrode, YSZ as the electrolyte, MgO as a substrate tube, a cylindrical high-temperature steam electrolysis cell using an MgAl 2 O 4 spinel mixture The manufactured example is described below.
[0020]
A base tube is manufactured by sintering a mixture of MgO and MgAl 2 O 4 spinel into a cylinder having a porosity of 30 mm, a thickness of 2 mm, and an inner diameter of about 10 to 20 mm.
[0021]
In this case, the coefficient of thermal expansion of the electrode material between the higher temperature of the temperature at the time of manufacturing the cell or the temperature during operation and the room temperature was measured, and the coefficient of thermal expansion of the sintered body of the mixture of MgO and MgAl 2 O 4 was measured. The mixing ratio of MgO 2 and MgAl 2 O 4 spinel is adjusted so that the measured thermal expansion coefficient of the electrode material is equal to or slightly larger than the higher thermal expansion coefficient.
[0022]
In this embodiment, the maximum temperature during cell production is 1300-1400 ° C. while the temperature during cell operation is about 1000 ° C., so the coefficient of thermal expansion of the electrode material between 1400 ° C. and room temperature is measured. As a result, the thermal expansion coefficients of the Ni-YSZ fuel electrode and the La 1-x Sr x MnO 3 air electrode were both 1.2 × 10 −5 . Therefore, the base tube is adjusted so that the mixing ratio of MgO and MgAl 2 O 4 spinel becomes MgO: Al 2 O 3 = 83: 17 by weight ratio, and then the inner diameter is about 12 mm, the thickness is about 2 mm, and the thermal expansion coefficient is 1.2. A pipe shape of × 10 −5 was manufactured.
[0023]
The substrate tube outside the Ni-YSZ anode or La 1-x Sr x MnO 3 a (x = 0.1) air electrode was prepared by 100 [mu] m to 500 [mu] m approximately slurry coating, YSZ dense electrolyte membrane by subsequent EVD method Was formed, and finally, the remaining electrodes were formed to obtain unit cells. Table 1 below shows the conditions for forming each layer and the thickness of each layer.
[0024]
[Table 1]
[0025]
Next, FIG. 1 shows the result of measuring the residual stress in the circumferential direction for the prepared single cell.
[0026]
According to this, Ni-YSZ anode or La 1-x Sr x MnO 3 (x = 0.1) residual tensile stress acting on the air electrode and the outer electrode becomes less 20 MPa, whereby the electrode is deteriorated, damaged It will not be done.
[0027]
Further, no tensile residual stress is generated in the electrolyte layer, and a compressive residual stress of 600 MPa or more acts. However, the electrolyte layer is not damaged by the compressive residual stress.
[0028]
【The invention's effect】
In short, according to the present invention, in a four-layer cylindrical high-temperature steam electrolysis cell, the residual tensile stress acting on the electrode layer can be reduced to 1/10 or less of that of the conventional solid electrolyte fuel cell. Deterioration and damage can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circumferential residual stress in a cylindrical high-temperature steam electrolysis cell according to the present invention.
FIG. 2 is a view showing a residual stress in a circumferential direction in a conventional cylindrical high-temperature steam electrolysis cell having a four-layer structure.