JP7389420B2 - Porous solid electrolyte gas sensor - Google Patents
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- 239000007784 solid electrolyte Substances 0.000 title claims description 28
- 239000012528 membrane Substances 0.000 claims description 33
- 229910044991 metal oxide Inorganic materials 0.000 claims description 22
- 150000004706 metal oxides Chemical class 0.000 claims description 22
- 239000000758 substrate Substances 0.000 claims description 15
- 239000010416 ion conductor Substances 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 8
- 229910000510 noble metal Inorganic materials 0.000 claims description 8
- 229910001413 alkali metal ion Inorganic materials 0.000 claims description 5
- 230000003247 decreasing effect Effects 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 54
- 239000002228 NASICON Substances 0.000 description 31
- 230000004044 response Effects 0.000 description 26
- 238000010304 firing Methods 0.000 description 13
- 238000010586 diagram Methods 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 5
- 238000001514 detection method Methods 0.000 description 5
- WMWLMWRWZQELOS-UHFFFAOYSA-N bismuth(iii) oxide Chemical compound O=[Bi]O[Bi]=O WMWLMWRWZQELOS-UHFFFAOYSA-N 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000000635 electron micrograph Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910001415 sodium ion Inorganic materials 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- -1 30 wt% or less Chemical class 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 239000002227 LISICON Substances 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 229910003249 Na3Zr2Si2PO12 Inorganic materials 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 235000011187 glycerol Nutrition 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 150000002576 ketones Chemical class 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000001420 photoelectron spectroscopy Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 231100000572 poisoning Toxicity 0.000 description 1
- 230000000607 poisoning effect Effects 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 239000012855 volatile organic compound Substances 0.000 description 1
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Description
この発明は多孔質の固体電解質膜を用いるガスセンサに関する。 The present invention relates to a gas sensor using a porous solid electrolyte membrane.
起電力を応答出力とする通常の固体電解質型のガスセンサでは、固体電解質の緻密な焼結体を用いるので、製造工程が複雑になる。検知極と対極を同じ雰囲気に曝し、参照雰囲気を必要としない、混成電位型の検知機構でも、緻密な焼結体を用いることは変わらない。発明者らは、Na+イオン導電体のNASICON焼結体を用い、常温作動が可能なCOセンサを提案したが(特許文献1,2、非特許文献1)、同様な問題がある。このため、ガスセンサの小型化、製造工程の単純化、MEMSホットプレートへの搭載によるインテリジェント化は困難であった。
A typical solid electrolyte gas sensor that uses electromotive force as a response output uses a dense sintered solid electrolyte, which complicates the manufacturing process. Even in a mixed potential type detection mechanism in which the detection electrode and counter electrode are exposed to the same atmosphere and no reference atmosphere is required, a dense sintered body is still used. The inventors have proposed a CO sensor that can operate at room temperature using a NASICON sintered body of Na + ion conductor (
この発明の課題は、多孔質の固体電解質膜を用いる新しい構造のガスセンサを提供することにより、ガスセンサの製造工程を簡単化し、ガスセンサの小型化を容易にすることにある。 An object of the present invention is to provide a gas sensor with a new structure using a porous solid electrolyte membrane, thereby simplifying the manufacturing process of the gas sensor and facilitating miniaturization of the gas sensor.
この発明の多孔質固体電解質ガスセンサは、
基板あるいはマイクロホットプレートのヒータを備えた膜等の支持体と、
共に支持体上に固定されかつ組成が互いに異なる一対の電極と、
一対の電極を覆うように支持体上に固定された多孔質の固体電解質膜、とを備え、
前記一対の電極間の起電力を出力とする。
The porous solid electrolyte gas sensor of this invention is
a support such as a substrate or a membrane equipped with a micro-hot plate heater;
a pair of electrodes both fixed on a support and having different compositions;
A porous solid electrolyte membrane fixed on a support so as to cover a pair of electrodes,
The electromotive force between the pair of electrodes is output.
この発明のガスセンサでは、起電力を出力とするので、極く僅かな電流が固体電解質中を流れれば良い。このため固体電解質粒子がネックなどで接触していれば十分で、多孔質の固体電解質膜でもガスを検出できる。固体電解質膜は好ましくは多孔質のアルカリ金属イオン導電体膜で、室温でCO,H2等のガスを検出できる。 Since the gas sensor of the present invention outputs electromotive force, only a very small amount of current needs to flow through the solid electrolyte. Therefore, it is sufficient that the solid electrolyte particles are in contact with each other at a neck or the like, and gas can be detected even with a porous solid electrolyte membrane. The solid electrolyte membrane is preferably a porous alkali metal ion conductor membrane that can detect gases such as CO and H2 at room temperature.
一対の電極の少なくと一方に貴金属と金属酸化物とを含有させると、金属酸化物により電極間に起電力の差を生じさせることができる。特に、一方の電極にはCOとの接触により起電力が増加するように金属酸化物を混合し、他方の電極にはCOとの接触により起電力が減少するように別の種類の金属酸化物を含有させると、大きなガス応答が得られる。 When at least one of a pair of electrodes contains a noble metal and a metal oxide, a difference in electromotive force can be generated between the electrodes due to the metal oxide. In particular, one electrode is mixed with a metal oxide so that the electromotive force increases when it comes into contact with CO, and the other electrode is mixed with a metal oxide of another type so that the electromotive force decreases when it comes into contact with CO. By containing , a large gas response can be obtained.
好ましくは、MEMSマイクロホットプレートのヒータを備える膜を支持膜とする。この膜は基板に設けた空洞上に掛け渡されている。MEMSマイクロホットプレートを用いると他のセンサの集積化と駆動回路の集積化が容易である。またマイクロホットプレートのヒータを電極と固体電解質膜の焼成に用いることができる。
Preferably, a membrane provided with a heater of a MEMS micro hot plate is used as the supporting membrane. This membrane is spanned over a cavity provided in the substrate. Using a MEMS micro hot plate makes it easy to integrate other sensors and drive circuits. Further, a micro hot plate heater can be used for baking the electrode and solid electrolyte membrane.
以下に本発明を実施するための最適実施例を示す。 The best embodiments for carrying out the present invention are shown below.
ガスセンサの構造
図1~図13に実施例を示す。図1,図2はガスセンサ2の構造を示し、3はSi等の基板で、4はエッチングにより基板3に設けた空洞であり、空洞4の上部をダイアフラム状の支持膜6が覆っている。支持膜6は空洞4をダイアフラム状に覆うのではなく、空洞4上を架橋していても良い。支持膜6は1層あるいは多層の絶縁膜から成り、実施例では多層の絶縁膜の間に膜状のPtヒータ8を備えている。Si基板3~ヒータ8は、MEMSマイクロホットプレートを構成する。
Embodiments of the structure of the gas sensor are shown in FIGS. 1 to 13. 1 and 2 show the structure of a
支持膜6上に一対の電極10,11が成膜され、一方は検知極、他方は対極で、組成が異なる。電極10,11の膜厚は実施例では10μmとしたが、任意である。また電極10,11を覆うように、支持膜6上に多孔質NASICON膜12(以下単に、NASICON膜12と言う)が成膜されている。電極10,11の端部にパッド15,16が接続され、ヒータ8の両端にパッド17,18が接続され、パッド15~18に図示しないリード線をボンディングする。このようにして、電極10/11間の起電力を、ガスセンサ2の出力とする。なおパッド15~18等を、導電性のスルーホール等を介して、基板3の底面の配線へ接続してもよい。またヒータ8は電極10,11の一方を兼用してもよい。
A pair of
NASICON膜12は多孔質の厚膜で、膜厚は例えば10μm~5mm程度で、膜厚0.1~0.3mm程度の膜を用いたが、膜厚3mmでもガスセンサとして動作した。NASICON以外のアルカリ金属イオン導電体を用いてもよく、例えばNaイオン導電体とリチウムイオン導電体のLISICONは類似のアルカリ金属イオン導電体で、共に室温でのCO検出に用いることができる。さらに室温で導電性のあるイオン導電体であれば、アルカリ金属イオン導電体以外の多孔質固体電解質膜を用いても良い。
The NASICON
検知極と対極とで電極組成を変えることにより、CO,H2,アンモニア,硫化水素,アルコール,ケトン,炭化水素等のガスと、電極との反応が変化する。この結果、ガスへの応答が例えば起電力として発生する。電極は例えば一方がPt,Au,Rh,Pd等の貴金属で、他方がペロブスカイト等の金属酸化物でも良い。 By changing the electrode composition between the sensing electrode and the counter electrode, the reaction between the electrode and gases such as CO, H2, ammonia, hydrogen sulfide, alcohol, ketones, and hydrocarbons changes. As a result, a response to the gas occurs, for example as an electromotive force. For example, one electrode may be made of a noble metal such as Pt, Au, Rh, Pd, etc., and the other electrode may be made of a metal oxide such as perovskite.
検知極と対極を何れも貴金属を主成分とする電極(貴金属が例えば70wt%以上)とし、何れか一方に金属酸化物を混合(例えば30wt%以下で0.01wt%以上で、好ましくは30wt%以下で0.1wt%以上)すると、電極間に性質の差が生じ、ガスを検出できる。CO等の還元性ガスに対して正の起電力応答が生じるようにする金属酸化物には、Bi2O3,Cr2O3等があり、負の起電力応答が生じるようにする金属酸化物には、CeO2,V2O5,WO3,Ta2O3,In2O3等がある。なおこのことは特許文献2で公表済みである。好ましくは、一方の電極には正の起電力応答が生じる金属酸化物を少なくとも一種類混合し、他方の電極には負の起電力応答が生じる金属酸化物を少なくとも一種類混合する。
Both the sensing electrode and the counter electrode are electrodes whose main component is a noble metal (e.g., 70 wt% or more of the noble metal), and one of them is mixed with a metal oxide (e.g., 30 wt% or less, 0.01 wt% or more, preferably 30 wt% or less). (0.1wt% or more), a difference in properties occurs between the electrodes, and the gas can be detected. Metal oxides that cause a positive electromotive force response to reducing gases such as CO include Bi 2 O 3 and Cr 2 O 3 , and metal oxides that cause a negative electromotive force response. Examples include CeO 2 , V 2 O 5 , WO 3 , Ta 2 O 3 , In 2 O 3 , etc. Note that this has already been published in
ヒータ8は電極10,11とNASICON膜12の焼成に用い、実施例のガスセンサ2は室温で動作するので、ガス検出時にヒータ8を動作させる必要はない。ただし-40℃等の低温で動作させる場合、あるいは炭化水素、VOC等を検出する場合、ヒータ8を動作させても良い。MEMSマイクロホットプレートを用いるのは、ガスセンサ2上で電極10,11とNASICON膜12を焼成するためである。また温度センサ、湿度センサ等の他のセンサと集積化でき、またガスセンサの付帯回路と集積化できるためである。実施例では、MEMSガスセンサではなく、アルミナ基板上に電極10,11とNASICON膜12を設けた際のデータを示す。
The
ガスセンサの製造例とNASICON膜の構造
NASICON(Na3Zr2Si2PO12)粉末を調製し、グリセリンでペースト化した。電極材料ペーストとして、貴金属ペーストと金属酸化物粉末を混合し、あるいは単味の貴金属ペーストを用いた。アルミナ基板上に検知極と対極のペーストを塗布し、NASICONペーストをその上部から塗布し、乾燥した。乾燥後に基板を例えば空気中で焼成し、電極の焼成と、多孔質NASICON膜の成膜(焼成)を同時に行った。電極の焼成と多孔質NASICON膜の成膜は別々に行っても良い。焼成雰囲気等は任意で、多孔質のNASICON膜を成膜できればよい。
Manufacturing example of gas sensor and structure of NASICON membrane
NASICON (Na 3 Zr 2 Si 2 PO 12 ) powder was prepared and made into a paste with glycerin. As the electrode material paste, a mixture of noble metal paste and metal oxide powder, or a plain noble metal paste was used. Pastes for the sensing electrode and counter electrode were applied onto an alumina substrate, and NASICON paste was applied from above and dried. After drying, the substrate was fired, for example, in air, and the electrodes were fired and the porous NASICON film was formed (fired) at the same time. The firing of the electrode and the formation of the porous NASICON film may be performed separately. The firing atmosphere and the like are arbitrary, as long as a porous NASICON film can be formed.
電極組成はPtペーストと金属酸化物の重量比で示し、Ptペースト中のPt濃度は80~90wt%であった。例えばPt(15Bi2O3)はPtペーストが85wt%、Bi2O3が15wt%であることを示し、焼成後の電極組成としては、Ptが82~84wt%、Bi2O3が18~16wt%となる。 The electrode composition was expressed as the weight ratio of Pt paste and metal oxide, and the Pt concentration in the Pt paste was 80 to 90 wt%. For example, Pt (15Bi 2 O 3 ) indicates that Pt paste is 85wt% and Bi 2 O 3 is 15wt%, and the electrode composition after firing is 82 to 84 wt% of Pt and 18 to 16 wt% of Bi2O3. Become.
図3は下部に見えるアルミナ基板上のNASICON膜を示し、図4はNASICON膜を拡大して示す。焼成条件は900℃×30分間である。 Figure 3 shows the NASICON film on the alumina substrate visible at the bottom, and Figure 4 shows an enlarged view of the NASICON film. The firing conditions were 900°C x 30 minutes.
図5は、Pt(15Bi2O3)電極とNASICON膜の破断面を示し、図5の下部にアルミナ基板が見える。図6は、Pt(15Bi2O3)電極とその周囲を拡大して示す。焼成条件は900℃×30分間である。 Figure 5 shows the fractured surface of the Pt (15Bi 2 O 3 ) electrode and NASICON membrane, and the alumina substrate can be seen at the bottom of Figure 5. FIG. 6 shows an enlarged view of the Pt (15Bi 2 O 3 ) electrode and its surroundings. The firing conditions were 900°C x 30 minutes.
電極中の金属酸化物の移動
従来例のガスセンサとして、ディスク状のNASICON焼結体(空気中1100℃で4時間焼結)に、検知極(Pt(15Bi2O3))と対極(Pt)のペーストを塗布し、空気中700℃、800℃、900℃の各温度で、30分ずつ熱処理した。熱処理後の検知極と対極の組成をXPS(X-ray
photoelectron spectroscopy)により分析した。対極でのBiのピークを図7に示す。熱処理により検知極のBi濃度が低下し、800℃あるいは900℃で処理すると対極にBiが観察され、900℃では対極に高濃度のBiが観察された。電極に添加する金属酸化物の内で、Bi2O3,V2O5,WO3は比較的融点が低い、あるいは昇華しやすい材料である。そして図7は、電極に混合した金属酸化物は焼成により移動し得ることを示している。
Migration of metal oxides in electrodes A conventional gas sensor consists of a disk-shaped NASICON sintered body (sintered in air at 1100℃ for 4 hours), a sensing electrode (Pt (15Bi 2 O 3 )) and a counter electrode (Pt). The paste was applied and heat treated in air at temperatures of 700°C, 800°C, and 900°C for 30 minutes each. The composition of the sensing electrode and counter electrode after heat treatment was analyzed using XPS (X-ray
analyzed by photoelectron spectroscopy). Figure 7 shows the peak of Bi at the opposite electrode. The Bi concentration of the sensing electrode decreased with heat treatment, and when treated at 800°C or 900°C, Bi was observed on the counter electrode, and at 900°C, a high concentration of Bi was observed on the counter electrode. Among the metal oxides added to the electrode, Bi 2 O 3 , V 2 O 5 , and WO 3 are materials that have a relatively low melting point or are easily sublimed. And FIG. 7 shows that the metal oxide mixed in the electrode can be moved by firing.
焼成温度の影響
検知極をPt(15Bi2O3)、対極をPtとし、NASICON膜の焼成条件を、空気中800℃×30分(図8)、空気中1000℃×30分(図9)、及び空気中900℃×30分(図10)に変化させた。室温の乾燥雰囲気での、300ppmCOへの応答を示す。なお実施例では、特に断らない限り乾燥雰囲気でのガス応答を示す。温度は周囲温度を示し、ガスセンサは加熱せずに周囲の温度で動作させた。実施例では、ガスへの応答は電極間の起電力の変化である。焼成温度が800℃(図8)では起電力は不安定で、焼成温度が1000℃(図9)では小さなCO応答しか得られなかったが、焼成温度が900℃(図10)では大きなCO応答が得られた。これらのことは、NASICON膜の焼成温度は900℃付近が好ましいことを示している。以下では、焼成条件を空気中900℃×30分間に統一した。
Effect of firing temperature The sensing electrode was Pt (15Bi2O3) and the counter electrode was Pt, and the firing conditions for the NASICON film were 800℃ x 30 minutes in air (Figure 8), 1000℃ x 30 minutes in air (Figure 9), and air. The temperature was changed to 900°C for 30 minutes (Figure 10). The response to 300 ppm CO in a dry atmosphere at room temperature is shown. In the Examples, gas responses in a dry atmosphere are shown unless otherwise specified. Temperature indicates ambient temperature, and the gas sensor was operated at ambient temperature without heating. In embodiments, the response to the gas is a change in electromotive force between the electrodes. At a firing temperature of 800°C (Fig. 8), the electromotive force was unstable, and at a firing temperature of 1000°C (Fig. 9), only a small CO response was obtained, but at a firing temperature of 900°C (Fig. 10), a large CO response was obtained. was gotten. These facts indicate that the firing temperature of the NASICON film is preferably around 900°C. In the following, the firing conditions were unified to 900°C in air for 30 minutes.
ガス応答
図10~図12は300ppmCOへのガスセンサの応答を示す。前記の図10はPt(15Bi2O3)極と単味のPt極を組み合わせた際の結果を示し、図11はPt(15CeO2)極と単味のPt極を組み合わせた際の結果を、図12はPt(15Bi2O3)極とPt(15CeO2)極を組み合わせた際の結果を示す。測定温度は室温で、バックグラウンドは乾燥空気とした。COへの起電力応答が得られ、Pt(15Bi2O3)極とPt(15CeO2)極を組み合わせることにより応答が増加した(図12)。なお加湿空気をバックグラウンドとしても、CO応答が得られる。
Gas Response Figures 10-12 show the response of the gas sensor to 300 ppm CO. Figure 10 above shows the results when a Pt (15Bi 2 O 3 ) pole and a plain Pt pole are combined, and Figure 11 shows the results when a Pt (15CeO 2 ) pole and a plain Pt pole are combined. , FIG. 12 shows the results when Pt(15Bi 2 O 3 ) and Pt(15CeO 2 ) poles are combined. The measurement temperature was room temperature, and the background was dry air. An electromotive force response to CO was obtained, and the response was increased by combining the Pt(15Bi 2 O 3 ) and Pt(15CeO 2 ) poles (FIG. 12). Note that CO responses can be obtained even with humidified air as a background.
低温での応答
図13は、300ppmCOに対する、-10℃での応答を示す。電極はPt(15Bi2O3)極とPt(15CeO2)極の組み合わせで、-10℃でもCOへの応答が得られた。
Response at low temperature Figure 13 shows the response at -10°C to 300 ppm CO. The electrodes were a combination of Pt (15Bi 2 O 3 ) and Pt (15CeO 2 ) electrodes, and a response to CO was obtained even at -10°C.
ガスの検出モデル
ガスの検出モデルを、発明者は以下のように推定している。多孔質のNASICON膜を用いるため、NASICON膜と電極との界面までガスは拡散し、ここにNASICONと電極とガスの3相界面が発生する。三相界面では、空気中で酸素とNaイオンとの間に、(1)式の平衡反応が生じる。
2Na++1/2O2+2e- → Na2O (1)
Gas Detection Model The inventor estimates the gas detection model as follows. Because a porous NASICON membrane is used, gas diffuses to the interface between the NASICON membrane and the electrode, where a three-phase interface between NASICON, the electrode, and the gas occurs. At the three-phase interface, the equilibrium reaction of equation (1) occurs between oxygen and Na ions in the air.
2Na + +1/2O 2 +2e - → Na 2 O (1)
ここで雰囲気にCOが加わると、(2)式の平衡反応が加わり、電極電位は(1)式の反応と(2)式の反応がバランスする点で定まる。このため起電力はCO等のガスに依存する。
CO+Na2O → 2Na++2e-+CO2 (2)
When CO is added to the atmosphere, the equilibrium reaction of equation (2) is added, and the electrode potential is determined at the point where the reactions of equation (1) and (2) are balanced. Therefore, the electromotive force depends on gas such as CO.
CO + Na 2 O → 2Na + +2e - +CO 2 (2)
電極に金属酸化物を混合すると、(3)式で示す、金属酸化物の非化学量論的酸化還元反応が加わる。式中δは微少量を、Mは金属元素を表す。(3)式の平衡は、還元を受け難いCeO2等では式の左側にかたより、還元されやすいBi2O3, Cr2O3等では式の右側にかたよる。このため単味のPt電極との間に起電力の差が生じ、しかも起電力の差は雰囲気中のガスに依存すると考えられる。
MOx+2δNa++2δe- → MOx-δ+δNa2O (3)
When a metal oxide is mixed into the electrode, a non-stoichiometric redox reaction of the metal oxide is added, as shown in equation (3). In the formula, δ represents a minute amount, and M represents a metal element. The equilibrium in equation (3) shifts to the left side of the equation for substances such as CeO2, which are difficult to reduce, and shifts to the right side of the equation for substances that are easily reduced, such as Bi2O3 and Cr2O3. For this reason, a difference in electromotive force occurs between the electrode and a single Pt electrode, and it is thought that the difference in electromotive force depends on the gas in the atmosphere.
MO x +2δNa + +2δe - → MO x-δ +δNa 2 O (3)
作用効果
実施例の作用効果を示す。
1) 膜状の固体電解質を用いるため、ガスセンサの小型化と集積化が容易である(図1,図2)。このことは、起電力を出力とし、固体電解質に必要な電気伝導度が低いため、可能になっている。
2) 特にMEMSマイクロホットプレートのヒータ付きの絶縁膜を支持膜とすると、他のセンサと集積化したり、制御回路を集積化することが容易になる。またホットプレートのヒータを電極と多孔質固体電解質膜の成膜に用いることができる。
3) 多孔質の固体電解質膜内をガスが拡散し、固体電解質と支持膜の間に電極を設けても、ガスを検出できる(図10~図12)。
4) 固体電解質膜としてアルカリイオン導電体を用い、ヒータによる加熱無しセンサを動作させると、CO、H2、アンモニア、硫化水素、エタノール、アセトン等の反応性が高いガスを検出する際に、アルカリイオン導電体中でガスが酸化されない。
5) 低温でも、ヒータを作動させずにCOを検出できる(図13)。
6) 電極に混合する金属酸化物は熱処理により移動する(図7)。電極を支持体(基板あるいは実施例の支持膜)と固体電解質膜の間に設けると、電極中の金属酸化物の移動を少なくできる。
7) 多孔質の固体電解質膜が雰囲気中の被毒成分をトラップするため、電極は被毒を受け難い。
Effects The effects of the examples are shown.
1) Since a membrane-like solid electrolyte is used, the gas sensor can be easily miniaturized and integrated (Figures 1 and 2). This is possible because the output is electromotive force and the solid electrolyte has low electrical conductivity.
2) In particular, if the insulating film with the heater of the MEMS micro-hot plate is used as the supporting film, it will be easy to integrate it with other sensors and control circuits. Further, a hot plate heater can be used for forming the electrode and the porous solid electrolyte membrane.
3) Gas diffuses within the porous solid electrolyte membrane, and gas can be detected even if an electrode is provided between the solid electrolyte and the support membrane (Figures 10 to 12).
4) When an alkali ion conductor is used as the solid electrolyte membrane and the sensor is operated without heating, the alkali ion Gases are not oxidized in the conductor.
5) CO can be detected even at low temperatures without activating the heater (Figure 13).
6) The metal oxide mixed into the electrode moves through heat treatment (Figure 7). When the electrode is provided between the support (the substrate or the support membrane in the example) and the solid electrolyte membrane, the movement of metal oxides in the electrode can be reduced.
7) The porous solid electrolyte membrane traps poisonous components in the atmosphere, making the electrodes less susceptible to poisoning.
2 ガスセンサ
3 Si基板
4 空洞
6 支持膜
8 ヒータ
10,11 電極
12 多孔質NASICON膜
15~18 パッド
2
Claims (4)
共に支持体上に固定されかつ組成が互いに異なる一対の電極と、
前記一対の電極を覆うように前記支持体上に固定された多孔質の固体電解質膜、とを備え、
前記一対の電極間の起電力を出力とするように構成され、
前記固体電解質膜は多孔質のアルカリ金属イオン導電体膜であり、
前記の一対の電極の少なくとも一方が貴金属と金属酸化物とを含有する、多孔質固体電解質ガスセンサ。 a support and
a pair of electrodes both fixed on a support and having different compositions;
a porous solid electrolyte membrane fixed on the support so as to cover the pair of electrodes,
configured to output an electromotive force between the pair of electrodes ,
The solid electrolyte membrane is a porous alkali metal ion conductor membrane,
A porous solid electrolyte gas sensor , wherein at least one of the pair of electrodes contains a noble metal and a metal oxide .
一対の電極の一方はCOとの接触により起電力が増加し、一対の電極の他方はCOとの接触により起電力が減少することを特徴とする、請求項1の多孔質固体電解質ガスセンサ。 The pair of electrodes both contain a noble metal and a metal oxide, and the types of metal oxides are different between the pair of electrodes,
2. The porous solid electrolyte gas sensor according to claim 1 , wherein one of the pair of electrodes has an increased electromotive force upon contact with CO, and the other of the pair of electrodes has an electromotive force that has decreased upon contact with CO.
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JP2000338081A (en) | 1999-05-28 | 2000-12-08 | Matsushita Electric Ind Co Ltd | Gas sensor |
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JP2791473B2 (en) * | 1988-02-12 | 1998-08-27 | フィガロ技研株式会社 | Gas detection method and device |
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JP2000338081A (en) | 1999-05-28 | 2000-12-08 | Matsushita Electric Ind Co Ltd | Gas sensor |
JP2001004589A (en) | 1999-06-23 | 2001-01-12 | Matsushita Electric Ind Co Ltd | Gas sensor |
JP2009128184A (en) | 2007-11-22 | 2009-06-11 | Figaro Eng Inc | Co2 sensor |
JP2011232291A (en) | 2010-04-30 | 2011-11-17 | Tdk Corp | Gas sensor |
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