JP3972822B2

JP3972822B2 - Gas sensor and fuel cell system using the same

Info

Publication number: JP3972822B2
Application number: JP2003013817A
Authority: JP
Inventors: 明信森山
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2003-01-22
Filing date: 2003-01-22
Publication date: 2007-09-05
Anticipated expiration: 2023-01-22
Also published as: JP2004226213A

Description

【０００１】
【発明の属する技術分野】
本発明は、被測定ガス中の酸素濃度、水素濃度を検出するガスセンサ及びこれを用いた燃料電池システムに関する。
【０００２】
【従来の技術】
被測定ガス中に特定成分を検出するガスセンサとして、酸素イオン伝導性固体電解質を用いたものやプロトン伝導性固体電解質を用いたものが知られている。
【０００３】
酸素イオン伝導性固体電解質を用いたセンサとしては、自動車の排気中の酸素濃度を検出する酸素濃度センサや酸素濃度から空燃比を求める空燃比センサ等がある（例えば、非特許文献１、２参照）。
【０００４】
また、このような酸素イオン伝導性固体電解質を用いたセンサは、酸素以外のガスにも反応することから、水素濃度を検出する場合にも適用されている（例えば、特許文献１参照）。
【０００５】
一方、プロトン伝導性固体電解質を用いたセンサとしては、被測定ガス中の水素濃度を検出する水素濃度センサが提案されている（例えば、特許文献２、３参照）。
【０００６】
【特許文献１】
特開２０００−９６８５号公報
【特許文献２】
特公平７−３１１５３号公報
【特許文献３】
特開２００２−３１０９７８号公報
【非特許文献１】
ＳＡＥペーパー（Ｎｏ．８５０３７８）
【非特許文献２】
自動車技術Ｖｏｌ．４１、Ｎｏ．１２、１９８７、ｐ．１４１４−１４１８
【０００７】
【発明が解決しようとする課題】
ところで、近年、高効率かつクリーンな動力源として盛んに研究開発が行われている「燃料電池（発電）システム」においては、低温（例えば、２００℃以下）であっても安定して動作するガスセンサが望まれている。
【０００８】
しかし、前記酸素イオン伝導性固体電解質を用いたセンサは、５００〜９００℃という高温でしか安定して動作しないため、「燃料電池システム」には適用することができず、また、前記プロトン伝導性固体電解質を用いたセンサは、低温で動作するものの、酸素濃度を検出するものは存在しなかった。
【０００９】
本発明は、このような従来の問題を解決するためになされたものであり、低温で安定して動作し、被測定ガス中の酸素濃度を精度よく検出できるガスセンサ及びこれを用いた燃料電池システムを提供することを目的とする。
【００１０】
【課題を解決するための手段】
このため、本発明に係る第１のガスセンサは、被測定ガスを制限して測定室内に拡散流入させる拡散律速手段と、水素含有成分から分離した水素を前記測定室に輸送する水素輸送手段と、輸送された水素と前記測定室内に流入した被測定ガス中の酸素とを反応させる酸化反応手段と、前記測定室内の水素濃度を検出する水素濃度検出手段と、を備え、前記測定室内の水素濃度が所定濃度になるように前記測定室に輸送する水素量を制御し、この水素輸送量に基づいて前記被測定ガス中の酸素濃度を検出するようにした。
【００１１】
また、本発明に係る第２のガスセンサは、燃料電池セルの酸素極側のガスを制限して第１測定室内に拡散流入させる第１拡散律速手段と、燃料電池セルの水素極側のガスを制限して第２測定室内に拡散流入させる第２拡散律速手段と、前記第２測定室から前記第１測定室に水素を輸送する水素輸送手段と、輸送された水素と前記第１測定室内に流入した被測定ガス中の酸素とを反応させる酸化反応手段と、前記第１測定室内の水素濃度を検出する第１水素濃度検出手段と、前記第２測定室内の水素濃度を検出する第２水素濃度検出手段と、を備え、前記第１測定室内の水素濃度が所定濃度となるように前記第１測定室に輸送する水素量を制御したときに、この水素輸送量に基づいて前記酸素極側の被測定ガス中の酸素濃度を検出する一方、前記第２測定室内の水素濃度が所定濃度となるように前記第１測定室に輸送する水素量を制御したときに、この水素輸送量に基づいて前記水素極側の被測定ガス中の水素濃度を検出するようにした。
【００１２】
また、本発明に係る燃料電池システムは、燃料ガスの経路に請求項１〜請求項１６のいずれか１つに記載のガスセンサを備えるようにした。
【００１３】
【発明の効果】
本発明に係る第１のガスセンサによると、酸素濃度を所定濃度（例えば、ほぼ０）とした測定室内には被測定ガスが拡散流入するが、このときの酸素量は前記被測定ガス中の酸素濃度に依存し、この拡散流入した被測定ガス中の酸素と輸送された水素とが反応（酸化反応）することによって前記測定室内の水素濃度が決定する。従って、水素輸送量が多い（対酸素量）と前記測定室内の水素濃度は高くなり、逆に水素輸送量が少ない（対酸素量）と前記測定室内の水素濃度は低くなる。ここで、水素輸送量は、前記測定室内の水素濃度が所定濃度（例えば、ほぼ０）となるように制御されるので、この水素輸送量が前記測定室に流入した酸素量を示すことになり、水素輸送量に基づいて被測定ガス中の酸素濃度を検出することができる。
【００１４】
このように、水素濃度が所定濃度となるように制御した水素輸送量に基づいて被測定ガス中の酸素濃度を検出できるので、比較的低温で動作するプロトン伝導性固体電解質体を用いて酸素濃度を検出できるガスセンサを得ることができる。これにより、ガスセンサを加熱するヒータ等の加熱手段を必要とせず、比較的低温（常温）から酸素濃度を検出できる。
【００１５】
また、本発明に係る前記第２のガスセンサによれば、酸素濃度を所定濃度（例えば、ほぼ０）とした第１測定室内には（燃料電池セルの）酸素極側の被測定ガスが拡散流入するが、このときの酸素量は酸素極側の被測定ガス中の酸素濃度に依存し、この拡散流入した酸素極側のガス中の酸素と輸送された水素とが反応（酸化反応）することによって前記第１測定室内の水素濃度が決定する。
【００１６】
一方、水素濃度を所定濃度（例えば、ほぼ０）とした第２測定室内には（燃料電池システムの）水素極側の被測定ガスが拡散流入するが、このときの水素量は水素極側の被測定ガス中の水素濃度に依存する。
【００１７】
従って、前記第１測定室内の水素濃度が所定濃度（例えば、ほぼ０）となるよう水素輸送量を制御すれば、前記第１のガスセンサと同様、このとき水素輸送量から酸素極側のガス中の酸素濃度を検出することができ、前記第２測定室内の水素濃度が所定濃度（例えば、ほぼ０）となるよう水素輸送量を制御すれば、このときの水素輸送量から水素極側のガス中の水素濃度を検出できる。
【００１８】
これにより、例えば燃料電池システムにおける重要なガスである酸素及び水素の濃度を１つのガスセンサによって検出することができ、コストの低減を図ることができる。
【００１９】
また、本発明に係る燃料電池システムによれば、重要なガスである酸素及び水素濃度のいずれか又は双方を検出できるので、酸素濃度、水素濃度を一定に制御して燃料電池システムの運転効率や過渡応答性などの性能向上が図れる。
【００２０】
【発明の実施の形態】
以下、本発明の実施形態を図に基づいて説明する。
図１は、本発明の第１実施形態に係るガスセンサ１００のセンサ素子の断面図である。図１において、被測定ガス１に接するように配置されたセンサ素子は、上側支持体１１及び下側支持体２１でプロトン伝導性固体電解質体（例えば、Ｎａｆｉｏｎ（デュポン社の登録商標）、以下、単に電解質体という）１０を挟持し、この電解質体１０の両表面上に、第１電極１３ａ、第２電極２３ａ、第３電極１４ａ及び第４電極２４ａを備えて構成される。これらの電極は、ＰｔあるいはＰｔを含む合金を担持した多孔質体から形成されて触媒機能を有しており、後述するように、前記第１電極１３ａが本発明に係る酸化反応手段に相当する。
【００２１】
第１電極（測定室側電極）１３ａは、上側支持体１１側に形成された第１空室（測定室）１３内に配置されており、第２電極（水素含有成分側電極）２３ａは、電解質体１０を挟んで第１空室１３に対向するよう下側支持体２１形成された第２空室内２３内に配置されている。
【００２２】
また、第３電極１４ａは、連通路１５を介して第１空室１３と連通するよう上側支持体１１側に形成された第３空室１４内に配置されており、第４電極２４ａは、電解質体１０を挟んで第３空室１４に対向するよう下側支持体２１に形成された第４空室２４内に配置されている。
【００２３】
また、上側支持体１１には、被測定ガス１を第１空室１３内に流入させるための第１被測定ガス導入孔１２が所定の拡散抵抗を有して形成されている。かかる第１被測定ガス導入孔１２が本発明における拡散律速手段に相当し、本実施形態においては、前記第１被測定ガス導入孔１２を微細な孔として形成しているが、例えば多孔質なアルミナセラミックス等の多孔質体によって形成するようにしてもよい。
【００２４】
下側支持体２１には、被測定ガス１を第２空室２３内に導くための第２被測定ガス導入孔２２が、前記第１被測定ガス導入孔１２よりも十分に大きな孔として形成されている。
【００２５】
そして、被測定ガス１は、拡散制限されつつ、第１被測定ガス導入孔１２から第１空室１３内に導かれて第１電極１３ａに到達する。更に、連通路１５を介して第３空室１４へも導かれる。また、被測定ガス１は、第２被測定ガス導入孔２２から第２空室２３内に導かれて第２電極２３ａに到達する。なお、第４空室２４は、他の空室や被測定ガス導入孔とは連通しておらず、ほぼ密封に近い状態となっている。
【００２６】
更に、第３空室１４の水素分圧（濃度）Ｐ１を検出する水素センシング回路３０が、第３電極１４ａと基準電極としての第４電極２４ａとの間で電気的に接続されて設けられており、また、第１電極１３ａと第２電極２３ａとの間には、第１空室１３内にプロトン（Ｈ⁺）を輸送できるように、水素ポンピング回路４０が設けられている。
【００２７】
前記水素センシング回路３０は、第３電極１４ａと第４電極２４ａ間の水素濃度の差によって発生する起電力を検出し、この起電力に基づいて第３空室１４の水素分圧(濃度)Ｐ１を検出する。なお、かかる水素センシング回路３０、第３電極１４ａ及び第４電極２４ａが本発明に係る水素濃度検出手段に相当する。
【００２８】
前記水素ポンピング回路４０は、第１電極１３ａと第２電極２３ａ間に所定電圧を印加することにより第２電極２３ａにおいてプロトンを発生させる共に、発生したプロトンが第２電極２３ａ側から第１電極側１３ａ側へと移動するときに流れる電流（水素ポンピング電流Ｉｐ）を検出する。なお、かかる水素ポンピング回路４０、第１電極１３ａ及び第２電極２３ａが本発明に係る水素輸送手段に相当する。
【００２９】
ここで、以上のように構成されたセンサ素子１００を有するガスセンサによる酸素濃度の検出について説明する。
被測定ガス１中の酸素は、所定の拡散抵抗を有する第１被測定ガス導入孔１２によって拡散制限されて第１空室１３内に流入する。このときの酸素流入量は、被測定ガス１中の酸素濃度Ｃ１と第１空室１３内（連通路１５内又は第３空室１４内としても同じである）の酸素濃度Ｃ２との濃度差に依存するから、第１空室１３内の酸素濃度Ｃ２を一定（例えば、ほぼ０とする）とすれば、被測定ガス１中の酸素濃度Ｃ１に依存した量の酸素が第１空室１３内に流入することになる。
【００３０】
そして、酸素濃度Ｃ２をほぼ０とした第１空室１３内に、拡散制限されて流入する酸素量に応じた量の水素を、同じく第１空室１３内に輸送（導入）することができれば、酸化触媒としての機能を有する第１電極１３ａ上で酸化反応が生じ、再び第１空室１３内の酸素濃度Ｃ２をほぼ０（すなわち、被測定ガス１の流入前と同じ状態）とすることができる。このとき導入した水素量は、次式（１）に示すように、第１空室１３内に流入する酸素量の２倍の量となる。
【００３１】
２Ｈ₂＋Ｏ₂→２Ｈ₂Ｏ（１）
従って、第１空室１３内に導入した水素量（すなわち、水素輸送量）を求めることができれば、第１空室１３内に流入した酸素量、すなわち、被測定ガス１中の酸素濃度Ｃ１を求めることができることなる。
【００３２】
ここで、第１空室１３内への水素の導入、及び、被測定ガス１中の酸素濃度Ｃ１の検出について更に詳しく説明する。
例えば、燃料電池システムにおいては、燃料電池セル本体（スタック）の酸素極への供給ガスは、加湿空気であることが一般的であり、少なからず水分が存在する。そこで、本実施形態では、ガスセンサを燃料電池システムにおける酸素極配管に配置した場合を想定し、被測定ガス１中の水（水蒸気）から水素を分離して第１空室１３に導入するようにした。
【００３３】
具体的には、水素ポンピング回路４０によって第１電極１３ａと第２電極２３ａ間に所定電圧を印加することにより、第２被測定ガス導入孔２２から導入した被測定ガス１中の水（水蒸気）を第２電極２３ａ上で電気分解してプロトンを発生させる（イオン化する）。発生したプロトンは、電解質体１０を介して第１電極１３ａ側へと輸送されて（汲み出されて）、再び水素となって第１空室１３内に拡散する。なお、プロトン輸送量は、第１電極１３ａと第２電極２３ａ間の印加電圧を制御することで調整する。
【００３４】
このときの第２電極２３ａ上での反応（プロトンの発生）は、次式（２）で表され、この反応量（すなわち、プロトン輸送量）は、水素ポンピング回路４０によって水素ポンピング電流Ｉｐとして検出される。
【００３５】
Ｈ₂Ｏ→２Ｈ⁺＋Ｏ₂／２＋２ｅ^- （２）
そして、上記したように、水素量が酸素量の２倍必要であることを考慮しつつ、水素ポンピング電量Ｉｐと被測定ガス１中の酸素濃度Ｃ１との関係を表すと、次式（３）のようになる。
【００３６】
Ｉｐ＝２・ｎＦ／ＲＴ・Ｄ・Ｐ・Ａ／Ｌ・（Ｃ１−Ｃ２）（３）
但し、ｎ：電荷の数（水素＝２）、Ｆ：ファラデー定数、Ｒ：ガス定数、
Ｐ：ガス圧力、Ｄ：酸素の拡散係数、Ａ：拡散有効面積、Ｌ：拡散有効距離、
Ｃ１：被測定ガス１中の酸素濃度、Ｃ２：第１空室１３（＝連通路１５＝第３空室１４）内の酸素濃度である。なお、右辺の「２」は、水素量は酸素量の２倍必要であることを反映したものである。
【００３７】
上記式（３）より、第１空室１３（＝連通路１５＝第３空室１４）内の酸素濃度Ｃ２をほぼ０（分圧換算で１０^-10程度）とすれば、検出した水素ポンピング電流Ｉｐから被測定ガス１中の酸素濃度Ｃ１を求めることができる。
【００３８】
ここで、本実施形態では、後述するように、水素センシング回路３０の検出結果を水素ポンピング回路４０にフィードバックすることによって第１空室１３内の酸素濃度Ｃ２をほぼ０（すなわち、被測定ガス１が拡散流入する前の状態）に制御するようにしている。
【００３９】
なお、本実施形態における水素センシング回路３０は、図１に示すように、第３電極１４ａと第４電極２４ａとを両電極とした水素濃淡電池を形成しているが、第３電極１４ａに代えて第１電極１３ａとしても問題はない。
【００４０】
この水素濃淡電池の起電力Ｖｓは、次式（４）に示す「ネルンストの式」で表される。
Ｖｓ＝ＲＴ／２Ｆ・ｌｎ（Ｐ４／Ｐ１）（４）
但し、Ｐ１：第３電極１４ａ（＝第１電極１３ａ）上の水素分圧、Ｐ４：第４電極２４ａ上の水素分圧（基準分圧）
そして、水素濃淡電池の起電力Ｖｓは、図２に示すように、第３空室１４内（＝第１空室１３内）が水素リッチ時に高くなり、水素リーン時に低くなるという関係にあるが、酸素ではその逆となり、酸素リッチに低くなる酸素リーン時に高くなるという関係となる。
【００４１】
しかし、濃度と起電力との関係でみると逆とはなっているものの、上記式（１）に示した触媒反応によって、両者とも「ほぼ０」となるところで起電力Ｖｓが急変する特性を持つことから、この場合には、酸素濃度＝水素濃度として扱うことができる。
【００４２】
そこで、本実施形態においては、水素センシング回路３０の検出する起電力Ｖｓが、第３空室１４内（＝第１空室１３内）の水素濃度が「ほぼ０」となる値になるように、水素ポンピング回路４０を制御してプロトンを輸送することで第１空室１３内の酸素濃度Ｃ２を「ほぼ０」とし、このときの水素ポンピング電流Ｉｐ（すなわち、プロトン輸送量）から被測定ガス１中の酸素濃度Ｃ１を求めるようにしている（上記式（３）参照）。
【００４３】
これにより、低温で動作するプロトン伝導性固体電解質を用いて被測定ガス中の酸素濃度を精度よく検出できる。
なお、水素センシング回路３０において、基準となる第４空室２４内は比較的高濃度の水素雰囲気とする必要があるが、第２電極２３ａから第４電極２４ａに僅かな水素を輸送するようにすることで容易に作り出せる。
【００４４】
更に、上記式（３）において、酸素の拡散係数Ｄの圧力依存性や温度依存性によって、ガス圧力Ｐ及びガス温度Ｔの影響を完全に抑えることはできないため、被測定ガスの圧力Ｐ、温度Ｔのいずれか又は両方を別に測定し、この測定したガス圧力Ｐ及び／又はガス温度Ｔに応じて、上記のようにして検出した酸素濃度を補正するようにしてもよい。
【００４５】
以上説明した第１実施形態では、下記のような効果を有する。
電解質体１０と、第１電極１３ａと、第２電極２３ａと、を有し、第１電極１３ａと第２電極２３ａとに接続された水素ポンピング回路４０によって両電極間に電圧を印加することにより第２電極２３ａにてプロトンを発生させ、発生したプロトンを第１電極１３ａ側に輸送するので、この水素ポンピング回路４０（すなわち、両電極に印加する電圧）を制御することで第１空室１３に輸送する水素量を調整できる。
【００４６】
第１電極１３ａは酸化触媒としての機能を有するので、専用の構成を設けることなく、第１空室１３内に輸送された水素と拡散制限されて流入した酸素とを反応（酸化反応）させることができる。
【００４７】
電解質体１０と、第３電極１４ａ（又は第１電極１３ａ）と、第４電極（基準電極）２３ａと、を有し、第３電極１４ａ（又は第１電極１３ａ）と第４電極２３ａとに接続された水素センシング回路３０によって両極間の水素濃度に応じて発生する起電力を検出するので、輸送された水素量と拡散制限されて流入した酸素量との反応によって決定される第１空室１３内の水素濃度を検出できる。
【００４８】
水素含有成分を被測定ガス１中の水（水蒸気）とすることで、水素源を特別に設けることなく、また、被測定ガス中に水素が存在しない場合でも酸素濃度を検出できる。
【００４９】
検出した酸素濃度を、被測定ガスの圧力及び温度の少なくとも一方に応じて補正するので、原理上、僅かながら受けるガス圧力、ガス温度の影響を考慮した検出精度を向上できる。
【００５０】
次に、第２実施形態について説明する。
図３は、本発明の第２実施形態に係るガスセンサ２００のセンサ素子の断面図である。なお、図３において、前記第１実施形態(図１）と同一部分については同一の符号とし、その説明は省略する。
【００５１】
この実施形態は、第１空室１３内に流入した酸素と反応させる水素を大気中の水蒸気とした点が前記第１実施形態と異なる。大気中には、少なからず水蒸気が存在しており、この水蒸気が第１実施形態における被測定ガス１中の水蒸気と同様に、第１電極１３ａ側にプロトンを輸送するための水素源となり得る。このため、第２実施形態におけるセンサ素子部は、図３に示すように、第２電極２３ａが、被測定ガス１から隔絶するように設けられた大気導入路２２に接触する構造を特徴としている。また、この大気導入路２２に代えて、図示しない燃料電池システムの水素極ラインと連通させた水素導入路としても同様の効果を得ることができる。
【００５２】
かかる第２実施形態では、水素含有成分を被測定ガスと隔絶された大気中の水（水蒸気）とするか、あるいは、被測定ガスと隔絶された配管内の水素とするので、被測定ガス中に水素含有成分（水素、水蒸気等）が存在しない場合でも酸素濃度を検出できる。更に、水素含有成分を被測定ガスと隔絶された配管内の水素とした場合には、最もイオン化し易い水素を用いることから、プロトンの発生が容易であり、安定した検出を行うことができる。なお、被測定ガスと隔絶された配管としては、上述したように、例えば、燃料電池システムの燃料極（水素極）ラインの配管がある。
【００５３】
なお、本実施形態においても、被測定ガスの圧力Ｐ、温度Ｔのいずれか又は両方を別に測定し、この測定したガス圧力Ｐ及び／又はガス温度Ｔに応じて、検出した酸素濃度を補正するようにしてもよい。
【００５４】
次の第３実施形態について説明する。
図４は、本発明の第３実施形態に係るガスセンサ３００のセンサ素子の断面図である。図４においても、前記第１実施形態(図１)と同一部分については同一の符号とし、その説明は省略する。この実施形態は、図示しない燃料電池セルの酸素極ラインと水素極ラインとの両方のガス（Ｏ₂、Ｈ₂）を被測定ガス１としたものである。
【００５５】
図４において、右側支持体（前記上側支持体に相当する）１１には、燃料電池セルの酸素極側と連通する酸素極ライン１６が形成されており、左側支持体（前記下側支持体に相当する）２１には、燃料電池セルの水素極側と連通する水素極ライン２６が形成されている。なお、この実施形態では、水素極ライン２６と連通する第２被測定ガス導入孔（第２拡散律速手段に相当する）２２も、酸素極ライン１６と連通する第１被測定ガス導入孔（第１拡散律速手段）１２と同様、所定の拡散抵抗を有する（拡散律速を与える）ように形成されている。
【００５６】
また、前記第１、２実施形態とは異なり、連通路１５を有しておらず、各電極（１３ａ、１４ａ、２３ａ、２４ａ）がそれぞれ隔離された空室（符号省略）内に配置され、第３電極１４ａが第２電極２３ａに対する基準電極を、第４電極２４ａが第１電極１３ａに対する基準電極を構成する。
【００５７】
更にまた、第１電極１３ａ側の水素分圧（濃度）を検出する第１水素センシング回路３１が、第１電極１３ａと第４電極（基準電極）２４ａとの間で電気的に接続されていると共に、第２電極２３ａ側の水素分圧（濃度）Ｐ２を検出する第２水素センシング回路３２が、第２電極２３ａと第３電極（基準電極）１４ａとの間で電気的に接続されている。すなわち、本実施形態では、第１水素センシング回路３１、第１電極１３ａ及び第４電極２４ａが本発明に係る第１水素濃度検出手段に相当し、第２水素センシング回路３２、第２電極２３ａ及び第３電極１４ａが本発明に係る第２水素濃度検出手段に相当する。なお、各電極側の濃度は、各電極が配置される空室内の濃度と同様の意味である。
【００５８】
ここで、まず、本実施形態における水素濃度の検出について説明する。
第２被測定ガス導入孔２２を介して第２電極２３ａ側（第２空室２３内）に拡散流入する水素量は、水素極ライン２６内の被測定ガス中の水素濃度Ｃ１'と第２電極２３ａ側の水素濃度Ｃ２'との濃度差に依存し、その量が制限される。従って、第２電極２３ａ側の水素濃度Ｃ２'をほぼ０（分圧換算１０^-10程度）とすれば、水素極ライン２６内の被測定ガス中の水素濃度Ｃ１'に依存した水素量が第２電極側２３ａに流入することになる。
【００５９】
そこで、第２水素センシング回路３２の検出する起電力（Ｖｓ−２）が、第２電極２３ａ側の水素濃度が「ほぼ０」となる値になるように、水素ポンピング回路４０を制御する。このときの水素ポンピング電流（Ｉｐ−２）は、次式（５）で表すことができる。
【００６０】
（Ｉｐ−２）＝（ｎＦ／ＲＴ）・Ｄ・Ｐ・Ａ／Ｌ・（Ｃ１'−Ｃ２'）（５）
上記式（５）において、第２電極２３ａ側の水素濃度Ｃ２'（≒０）であるから、検出した水素ポンピング電流（Ｉｐ−２）、すなわち、プロトン輸送量から水素極ライン２６内の被測定ガス中の水素濃度Ｃ１'を求めることができる。
【００６１】
次に、酸素濃度の検出について説明する。
本実施形態における酸素濃度の検出も、前記第１、２実施形態と基本的には同じである。すなわち、第１水素センシング回路３１の検出する起電力（Ｖｓ−１）が、第１電極１３ａ側（第１空室１３内）の水素濃度（＝酸素濃度）が「ほぼ０」となる値になるように、水素ポンピング回路４０を制御する。このときの水素ポンピング電流（Ｉｐ−１）は、上記式（３）と同様に、次式（６）のように表すことができる。
【００６２】
（Ｉｐ−１）＝２・ｎＦ／ＲＴ・Ｄ・Ｐ・Ａ／Ｌ・（Ｃ１−Ｃ２）（６）
但し、Ｃ１：酸素極ライン１６内の被測定ガス中の酸素濃度、Ｃ２：第１電極１３ａ側の酸素濃度（≒０）
これにより、検出した水素ポンピング電流（Ｉｐ−１）、すなわち、プロトン輸送量から酸素極ライン１６内の被測定ガス中の酸素濃度Ｃ１を求めることができる。
【００６３】
かかる第３実施形態では、水素ポンピング回路４０を第１水素センシング回路３１の検出結果に基づいて制御するか、第２水素センシング回路３２の検出結果に基づいて制御するか、を切り換えることによって、酸素極ライン１６側の被測定ガス中の酸素濃度と水素極ライン２６側の被測定ガス中の水素濃度とを１つのセンサで検出できる。
【００６４】
また、上記制御の切り換えは、必要に応じて設定した所定の時間間隔（例えば１秒前後の間隔）で行うようにしたり、燃料電池システムにおける必要性（要求）に応じて行うようにしたりすればよい。このように、酸素極ライン１６側の酸素濃度の検出と水素極ライン１６側の水素濃度の検出とを、所定時間毎又は燃料電池システムからの指令に基づいて切り換えることで、燃料電池システムにおいて重要な酸素濃度と水素濃度とを順次又は必要に応じて適宜検出できる。
【００６５】
なお、本実施形態においても、酸素極ライン１６内のガスの圧力、温度のいずれか又は双方を別に測定し、この測定した酸素極ライン１６内のガス圧力及び／又はガス温度に応じて検出した酸素濃度を補正したり、水素極ライン２６内のガスの圧力、温度のいずれか又は双方を別に測定し、この測定した水素極ライン２６内のガス圧力及び／又はガス温度に応じて検出した水素濃度を補正したりするようにしてもよい。
【００６６】
次に第４実施形態について説明する。
図５は、本発明の第４実施形態を示し、燃料電池セルとして用いられている電解質体の一部をガスセンサに流用するようにしたものを模式的に表したものである。前記第１〜３実施形態で使用しているプロトン伝導性固体電解質体１０は、燃料電池セル用の電解質体と同等のものであることから、この燃料電池セル用電解質体をガスセンサ用のプロトン伝導性固体電解質体１０として用いることができる。酸素濃度の検出、水素濃度の検出及びその補正については、すでに説明したものと同様であるので、ここでの説明は省略する。
【００６７】
なお、図５においては、燃料電池セル（スタック）の特定セルのガス入口部２ａとガス出口部２ｂとに、ガスセンサ４００を取り付けるようにしているが、ガスセンサ部と燃料電池の発電部とを電気的に切り離せば、セル内部の任意の部位におけるガス濃度（酸素濃度、水素濃度）を検出することも可能である。
【００６８】
かかる第４実施形態では、燃料電池に用いる（発電用の）プロトン伝導性固体電解質体の一部をガスセンサ用の電解質体として用いるので、発電用電解質体内のガス濃度を直接検出することができ、高応答な検出が可能となる。また、共用することによりコスト低減も図れると共に、燃料電池セルの一部を流用することで燃料電池セル（スタック）の任意の位置（ガス入口、ガス出口、セル内部）の酸素濃度、水素濃度を検出できる。
【００６９】
更に、以上説明したガスセンサのいずれかを燃料電池システムの燃料ガスラインに配置することで、燃料電池システムの主要成分である酸素ガス濃度や水素ガス濃度を精度よく検出し、これらのガス濃度情報から酸素供給流量制御や水素供給流量制御をさらに最適化させて、運転効率や過渡時の追従性等の性能向上を図ることができる。しかも、前記ガスセンサは、低温でも安定して動作するため、ヒータ等の過熱手段を備える必要がないから、燃料電池システムの安全性を損なうことがなく、また、その構成も簡単なものであるので比較的低コストで実現できる。
【図面の簡単な説明】
【図１】本発明に係るガスセンサの第１実施形態を示す図である。
【図２】第３空室１４（＝第１空室１３）内の水素濃度（酸素濃度）と起電力の関係を示す図である。
【図３】本発明に係るガスセンサの第２実施形態を示す図である。
【図４】本発明に係るガスセンサの第３実施形態を示す図である。
【図５】本発明に係るガスセンサの第４実施形態を示す図である。
【符号の説明】
１０…プロトン伝導性固体電解質体、１２、２２…被測定ガス導入孔、１３…第１空室、１３ａ…第１電極、１４…第３空室、１４ａ…第３電極、２３…第２空室、２３ａ…第２電極、２４…第４空室、２４ａ…第４電極、３０，３１，３２…水素センシング回路、４０…水素ポンピング回路、１００，２００，３００，４００…ガスセンサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor that detects an oxygen concentration and a hydrogen concentration in a gas to be measured, and a fuel cell system using the gas sensor.
[0002]
[Prior art]
As a gas sensor for detecting a specific component in a gas to be measured, one using an oxygen ion conductive solid electrolyte or one using a proton conductive solid electrolyte is known.
[0003]
Examples of the sensor using an oxygen ion conductive solid electrolyte include an oxygen concentration sensor that detects an oxygen concentration in an automobile exhaust, an air-fuel ratio sensor that obtains an air-fuel ratio from the oxygen concentration, and the like (for example, see Non-Patent Documents 1 and 2). ).
[0004]
Moreover, since the sensor using such an oxygen ion conductive solid electrolyte reacts also with gas other than oxygen, it is applied also when detecting hydrogen concentration (for example, refer patent document 1).
[0005]
On the other hand, as a sensor using a proton conductive solid electrolyte, a hydrogen concentration sensor that detects a hydrogen concentration in a gas to be measured has been proposed (see, for example, Patent Documents 2 and 3).
[0006]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2000-9985
[Patent Document 2]
Japanese Examined Patent Publication No. 7-31153
[Patent Document 3]
JP 2002-310978 A
[Non-Patent Document 1]
SAE paper (No. 850378)
[Non-Patent Document 2]
Automotive Technology Vol. 41, no. 12, 1987, p. 1414-1418
[0007]
[Problems to be solved by the invention]
By the way, in the “fuel cell (power generation) system” that has been actively researched and developed as a highly efficient and clean power source in recent years, a gas sensor that operates stably even at low temperatures (for example, 200 ° C. or lower). Is desired.
[0008]
However, since the sensor using the oxygen ion conductive solid electrolyte operates stably only at a high temperature of 500 to 900 ° C., it cannot be applied to the “fuel cell system”, and the proton conductivity Although the sensor using the solid electrolyte operates at a low temperature, there is no sensor that detects the oxygen concentration.
[0009]
The present invention has been made to solve such a conventional problem, and is a gas sensor that operates stably at a low temperature and can accurately detect an oxygen concentration in a gas to be measured, and a fuel cell system using the same. The purpose is to provide.
[0010]
[Means for Solving the Problems]
For this reason, the first gas sensor according to the present invention includes a diffusion rate-limiting means for restricting the gas to be measured and diffusing and flowing into the measurement chamber, a hydrogen transport means for transporting hydrogen separated from the hydrogen-containing component to the measurement chamber, An oxidation reaction means for reacting the transported hydrogen with oxygen in the gas to be measured flowing into the measurement chamber, and a hydrogen concentration detection means for detecting the hydrogen concentration in the measurement chamber, and the hydrogen concentration in the measurement chamber The amount of hydrogen transported to the measurement chamber was controlled so as to have a predetermined concentration, and the oxygen concentration in the gas to be measured was detected based on the amount of transported hydrogen.
[0011]
Further, the second gas sensor according to the present invention includes a first diffusion rate-limiting means for restricting the gas on the oxygen electrode side of the fuel cell and diffusing and flowing into the first measurement chamber; and a gas on the hydrogen electrode side of the fuel cell. A second diffusion rate-limiting means for limiting and allowing diffusion to flow into the second measurement chamber; a hydrogen transport means for transporting hydrogen from the second measurement chamber to the first measurement chamber; and the transported hydrogen and the first measurement chamber. Oxidation reaction means for reacting with oxygen in the gas to be measured, first hydrogen concentration detection means for detecting the hydrogen concentration in the first measurement chamber, and second hydrogen for detecting the hydrogen concentration in the second measurement chamber A concentration detecting means, and when the amount of hydrogen transported to the first measurement chamber is controlled so that the hydrogen concentration in the first measurement chamber becomes a predetermined concentration, the oxygen electrode side is controlled based on the hydrogen transport amount. While detecting the oxygen concentration in the measured gas, When the amount of hydrogen transported to the first measurement chamber is controlled so that the hydrogen concentration in the second measurement chamber becomes a predetermined concentration, the hydrogen concentration in the gas to be measured on the hydrogen electrode side is determined based on the hydrogen transport amount. It was made to detect.
[0012]
The fuel cell system according to the present invention includes the gas sensor according to any one of claims 1 to 16 in a fuel gas path.
[0013]
【The invention's effect】
According to the first gas sensor of the present invention, the gas to be measured diffuses and flows into the measurement chamber in which the oxygen concentration is a predetermined concentration (for example, approximately 0). At this time, the oxygen amount is the oxygen in the gas to be measured. Depending on the concentration, the concentration of hydrogen in the measurement chamber is determined by the reaction (oxidation reaction) between oxygen in the gas to be measured that has diffused and the transported hydrogen. Therefore, if the amount of hydrogen transport is large (the amount of oxygen), the hydrogen concentration in the measurement chamber increases. Conversely, if the amount of hydrogen transport is small (the amount of oxygen), the hydrogen concentration in the measurement chamber decreases. Here, since the hydrogen transport amount is controlled so that the hydrogen concentration in the measurement chamber becomes a predetermined concentration (for example, approximately 0), the hydrogen transport amount indicates the amount of oxygen flowing into the measurement chamber. The oxygen concentration in the gas to be measured can be detected based on the hydrogen transport amount.
[0014]
As described above, since the oxygen concentration in the gas to be measured can be detected based on the hydrogen transport amount controlled so that the hydrogen concentration becomes a predetermined concentration, the oxygen concentration is determined using a proton conductive solid electrolyte that operates at a relatively low temperature. Can be obtained. Thereby, a heating means such as a heater for heating the gas sensor is not required, and the oxygen concentration can be detected from a relatively low temperature (normal temperature).
[0015]
Further, according to the second gas sensor of the present invention, the gas to be measured on the oxygen electrode side (of the fuel cell) diffuses and flows into the first measurement chamber in which the oxygen concentration is a predetermined concentration (for example, approximately 0). However, the amount of oxygen at this time depends on the oxygen concentration in the gas to be measured on the oxygen electrode side, and the oxygen in the gas on the oxygen electrode side that has flowed in and the transported hydrogen react (oxidation reaction). Determines the hydrogen concentration in the first measurement chamber.
[0016]
On the other hand, the gas to be measured on the hydrogen electrode side (of the fuel cell system) diffuses and flows into the second measurement chamber where the hydrogen concentration is a predetermined concentration (for example, approximately 0). Depends on the hydrogen concentration in the gas to be measured.
[0017]
Therefore, if the hydrogen transport amount is controlled so that the hydrogen concentration in the first measurement chamber becomes a predetermined concentration (for example, approximately 0), as in the first gas sensor, the hydrogen transport amount in the gas on the oxygen electrode side is determined at this time. If the hydrogen transport amount is controlled so that the hydrogen concentration in the second measurement chamber becomes a predetermined concentration (for example, approximately 0), the gas on the hydrogen electrode side can be calculated from the hydrogen transport amount at this time. The hydrogen concentration inside can be detected.
[0018]
Thereby, for example, the concentration of oxygen and hydrogen, which are important gases in the fuel cell system, can be detected by one gas sensor, and the cost can be reduced.
[0019]
In addition, according to the fuel cell system of the present invention, since either or both of oxygen and hydrogen concentrations, which are important gases, can be detected, the operation efficiency of the fuel cell system is controlled by controlling the oxygen concentration and hydrogen concentration constant. Performance improvement such as transient response can be achieved.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view of a sensor element of a gas sensor 100 according to the first embodiment of the present invention. In FIG. 1, the sensor element disposed so as to be in contact with the gas 1 to be measured includes a proton conductive solid electrolyte body (for example, Nafion (registered trademark of DuPont), hereinafter) on the upper support 11 and the lower support 21. 10), and a first electrode 13a, a second electrode 23a, a third electrode 14a, and a fourth electrode 24a are provided on both surfaces of the electrolyte body 10. These electrodes are formed of a porous body carrying Pt or an alloy containing Pt and have a catalytic function. As will be described later, the first electrode 13a corresponds to the oxidation reaction means according to the present invention. .
[0021]
The first electrode (measurement chamber side electrode) 13a is disposed in the first vacant chamber (measurement chamber) 13 formed on the upper support 11 side, and the second electrode (hydrogen-containing component side electrode) 23a is It is disposed in a second chamber 23 formed with a lower support 21 so as to face the first chamber 13 across the electrolyte body 10.
[0022]
The third electrode 14a is disposed in the third vacant space 14 formed on the upper support 11 side so as to communicate with the first vacant space 13 through the communication path 15, and the fourth electrode 24a is It is arranged in a fourth chamber 24 formed in the lower support 21 so as to face the third chamber 14 across the electrolyte body 10.
[0023]
Further, a first measured gas introduction hole 12 for allowing the measured gas 1 to flow into the first vacant chamber 13 is formed in the upper support 11 with a predetermined diffusion resistance. The first measured gas introduction hole 12 corresponds to the diffusion-controlling means in the present invention. In the present embodiment, the first measured gas introduction hole 12 is formed as a fine hole. You may make it form with porous bodies, such as an alumina ceramic.
[0024]
In the lower support 21, a second measured gas introduction hole 22 for introducing the measured gas 1 into the second empty chamber 23 is formed as a sufficiently larger hole than the first measured gas introduction hole 12. Has been.
[0025]
Then, the gas to be measured 1 is guided from the first gas to be measured introduction hole 12 into the first vacant space 13 and reaches the first electrode 13a while being restricted in diffusion. Further, it is guided to the third vacant chamber 14 through the communication path 15. Further, the gas to be measured 1 is led from the second gas to be measured introduction hole 22 into the second empty chamber 23 and reaches the second electrode 23a. Note that the fourth vacant chamber 24 is not in communication with other vacant chambers or the gas-to-be-measured introduction hole, and is almost in a sealed state.
[0026]
Furthermore, a hydrogen sensing circuit 30 for detecting the hydrogen partial pressure (concentration) P1 of the third vacant chamber 14 is provided in an electrically connected manner between the third electrode 14a and the fourth electrode 24a as a reference electrode. In addition, between the first electrode 13a and the second electrode 23a, protons (H ⁺ ) Can be transported, a hydrogen pumping circuit 40 is provided.
[0027]
The hydrogen sensing circuit 30 detects an electromotive force generated by the difference in hydrogen concentration between the third electrode 14a and the fourth electrode 24a, and based on this electromotive force, the hydrogen partial pressure (concentration) P1 of the third vacant chamber 14 is detected. Is detected. The hydrogen sensing circuit 30, the third electrode 14a and the fourth electrode 24a correspond to the hydrogen concentration detecting means according to the present invention.
[0028]
The hydrogen pumping circuit 40 generates a proton in the second electrode 23a by applying a predetermined voltage between the first electrode 13a and the second electrode 23a, and the generated proton is transferred from the second electrode 23a side to the first electrode side. The current (hydrogen pumping current Ip) that flows when moving to the side 13a is detected. The hydrogen pumping circuit 40, the first electrode 13a, and the second electrode 23a correspond to the hydrogen transport means according to the present invention.
[0029]
Here, detection of the oxygen concentration by the gas sensor having the sensor element 100 configured as described above will be described.
Oxygen in the measured gas 1 is diffusion-limited by the first measured gas introduction hole 12 having a predetermined diffusion resistance and flows into the first empty chamber 13. At this time, the oxygen inflow amount is a difference in concentration between the oxygen concentration C1 in the gas 1 to be measured and the oxygen concentration C2 in the first vacant chamber 13 (which is the same in the communication passage 15 or the third vacant chamber 14). Therefore, if the oxygen concentration C2 in the first vacant chamber 13 is constant (for example, approximately 0), the amount of oxygen depending on the oxygen concentration C1 in the gas 1 to be measured 1 Will flow into.
[0030]
Then, if an amount of hydrogen corresponding to the amount of oxygen flowing in the first vacant space 13 with the oxygen concentration C2 being substantially zero can be transported (introduced) into the first vacant space 13 in the same way. Then, an oxidation reaction occurs on the first electrode 13a having a function as an oxidation catalyst, and the oxygen concentration C2 in the first vacant chamber 13 is set to almost 0 again (that is, the same state as before the measurement gas 1 flows in). Can do. The amount of hydrogen introduced at this time is twice as much as the amount of oxygen flowing into the first empty chamber 13, as shown in the following equation (1).
[0031]
2H ₂ + O ₂ → 2H ₂ O (1)
Therefore, if the amount of hydrogen introduced into the first vacant chamber 13 (that is, the amount of hydrogen transport) can be determined, the amount of oxygen flowing into the first vacant chamber 13, that is, the oxygen concentration C1 in the gas 1 to be measured is obtained. It can be obtained.
[0032]
Here, the introduction of hydrogen into the first vacant chamber 13 and the detection of the oxygen concentration C1 in the gas 1 to be measured will be described in more detail.
For example, in a fuel cell system, the supply gas to the oxygen electrode of the fuel cell main body (stack) is generally humid air, and there is a lot of moisture. Therefore, in the present embodiment, assuming that the gas sensor is disposed on the oxygen electrode pipe in the fuel cell system, hydrogen is separated from water (water vapor) in the gas 1 to be measured and introduced into the first empty chamber 13. did.
[0033]
Specifically, by applying a predetermined voltage between the first electrode 13a and the second electrode 23a by the hydrogen pumping circuit 40, water (water vapor) in the measured gas 1 introduced from the second measured gas introduction hole 22 is used. Is electrolyzed on the second electrode 23a to generate protons (ionize). The generated protons are transported (pumped out) to the first electrode 13 a side through the electrolyte body 10, and become hydrogen again and diffuse into the first empty chamber 13. The proton transport amount is adjusted by controlling the applied voltage between the first electrode 13a and the second electrode 23a.
[0034]
The reaction (proton generation) on the second electrode 23a at this time is expressed by the following equation (2), and this reaction amount (that is, proton transport amount) is detected as a hydrogen pumping current Ip by the hydrogen pumping circuit 40. Is done.
[0035]
H ₂ O → 2H ⁺ + O ₂ / 2 + 2e ^- (2)
Then, as described above, the relationship between the hydrogen pumping electric energy Ip and the oxygen concentration C1 in the gas 1 to be measured is expressed in consideration of the fact that the amount of hydrogen is twice as much as the amount of oxygen. become that way.
[0036]
Ip = 2.nF / RT.D.P.A / L. (C1-C2) (3)
Where n: number of charges (hydrogen = 2), F: Faraday constant, R: gas constant,
P: gas pressure, D: diffusion coefficient of oxygen, A: effective diffusion area, L: effective diffusion distance,
C1: oxygen concentration in the gas 1 to be measured, C2: oxygen concentration in the first empty chamber 13 (= communication path 15 = third empty chamber 14). Note that “2” on the right side reflects that the amount of hydrogen needs to be twice the amount of oxygen.
[0037]
From the above equation (3), the oxygen concentration C2 in the first vacant space 13 (= communication path 15 = third vacant space 14) is substantially 0 (10 in terms of partial pressure). ^-Ten The oxygen concentration C1 in the measured gas 1 can be obtained from the detected hydrogen pumping current Ip.
[0038]
Here, in the present embodiment, as described later, the oxygen concentration C2 in the first vacant chamber 13 is substantially zero (that is, the gas to be measured 1 by feeding back the detection result of the hydrogen sensing circuit 30 to the hydrogen pumping circuit 40. The state before the inflow of diffusion).
[0039]
As shown in FIG. 1, the hydrogen sensing circuit 30 in the present embodiment forms a hydrogen concentration cell using the third electrode 14a and the fourth electrode 24a as both electrodes. However, the hydrogen sensing circuit 30 is replaced with the third electrode 14a. There is no problem even if the first electrode 13a is used.
[0040]
The electromotive force Vs of the hydrogen concentration cell is expressed by the “Nernst equation” shown in the following equation (4).
Vs = RT / 2F · ln (P4 / P1) (4)
However, P1: Hydrogen partial pressure on the third electrode 14a (= first electrode 13a), P4: Hydrogen partial pressure on the fourth electrode 24a (reference partial pressure)
As shown in FIG. 2, the electromotive force Vs of the hydrogen concentration cell is high when the third vacant chamber 14 (= in the first vacant chamber 13) is rich in hydrogen and low when the hydrogen is lean. In the case of oxygen, the reverse is true, and the oxygen concentration becomes higher when the oxygen lean becomes lower.
[0041]
However, although the reverse is seen in the relationship between the concentration and the electromotive force, the electromotive force Vs suddenly changes when both become “nearly 0” by the catalytic reaction shown in the above formula (1). Therefore, in this case, it can be handled as oxygen concentration = hydrogen concentration.
[0042]
Therefore, in the present embodiment, the electromotive force Vs detected by the hydrogen sensing circuit 30 is set so that the hydrogen concentration in the third vacancy 14 (= in the first vacancy 13) becomes “approximately 0”. Then, by controlling the hydrogen pumping circuit 40 to transport protons, the oxygen concentration C2 in the first vacant chamber 13 is set to “almost 0”, and the gas to be measured is determined from the hydrogen pumping current Ip (ie, proton transport amount) at this time. 1 is obtained (see the above formula (3)).
[0043]
Thereby, the oxygen concentration in the gas to be measured can be accurately detected using the proton conductive solid electrolyte that operates at a low temperature.
In the hydrogen sensing circuit 30, the reference fourth vacancy 24 needs to have a relatively high concentration hydrogen atmosphere, but a small amount of hydrogen is transported from the second electrode 23 a to the fourth electrode 24 a. Can be easily created.
[0044]
Furthermore, in the above equation (3), the influence of the gas pressure P and the gas temperature T cannot be completely suppressed due to the pressure dependence and temperature dependence of the oxygen diffusion coefficient D. Either or both of T may be measured separately, and the oxygen concentration detected as described above may be corrected in accordance with the measured gas pressure P and / or gas temperature T.
[0045]
The first embodiment described above has the following effects.
By applying a voltage between both electrodes by the hydrogen pumping circuit 40 having the electrolyte body 10, the first electrode 13a, and the second electrode 23a, and connected to the first electrode 13a and the second electrode 23a. Protons are generated at the second electrode 23a, and the generated protons are transported to the first electrode 13a side. Therefore, by controlling this hydrogen pumping circuit 40 (that is, the voltage applied to both electrodes), the first vacancy 13 The amount of hydrogen transported to can be adjusted.
[0046]
Since the first electrode 13a has a function as an oxidation catalyst, the hydrogen transported into the first vacant chamber 13 and the oxygen that has flowed in are allowed to react (oxidation reaction) without providing a dedicated configuration. Can do.
[0047]
The electrolyte body 10, the third electrode 14a (or the first electrode 13a), and the fourth electrode (reference electrode) 23a, and the third electrode 14a (or the first electrode 13a) and the fourth electrode 23a Since the electromotive force generated according to the hydrogen concentration between the two electrodes is detected by the connected hydrogen sensing circuit 30, the first vacancy determined by the reaction between the amount of transported hydrogen and the amount of oxygen that flows in while being diffusion limited The hydrogen concentration in 13 can be detected.
[0048]
By making the hydrogen-containing component water (steam) in the gas 1 to be measured, it is possible to detect the oxygen concentration without specially providing a hydrogen source and when no hydrogen is present in the gas to be measured.
[0049]
Since the detected oxygen concentration is corrected according to at least one of the pressure and temperature of the gas to be measured, in principle, the detection accuracy can be improved in consideration of the effects of the gas pressure and gas temperature that are slightly received.
[0050]
Next, a second embodiment will be described.
FIG. 3 is a cross-sectional view of the sensor element of the gas sensor 200 according to the second embodiment of the present invention. In FIG. 3, the same parts as those in the first embodiment (FIG. 1) are denoted by the same reference numerals, and the description thereof is omitted.
[0051]
This embodiment is different from the first embodiment in that hydrogen to be reacted with oxygen flowing into the first empty chamber 13 is water vapor in the atmosphere. In the atmosphere, there is a considerable amount of water vapor, and this water vapor can be a hydrogen source for transporting protons to the first electrode 13a side, similarly to the water vapor in the gas 1 to be measured in the first embodiment. For this reason, as shown in FIG. 3, the sensor element section in the second embodiment is characterized by a structure in which the second electrode 23 a is in contact with the air introduction path 22 provided so as to be isolated from the gas 1 to be measured. . In addition, the same effect can be obtained by replacing the air introduction path 22 with a hydrogen introduction path communicating with a hydrogen electrode line of a fuel cell system (not shown).
[0052]
In the second embodiment, the hydrogen-containing component is water in the atmosphere (water vapor) isolated from the gas to be measured, or hydrogen in a pipe isolated from the gas to be measured. Even when there are no hydrogen-containing components (hydrogen, water vapor, etc.), the oxygen concentration can be detected. Further, when the hydrogen-containing component is hydrogen in a pipe isolated from the gas to be measured, hydrogen that is most easily ionized is used, so that protons can be easily generated and stable detection can be performed. As described above, the piping isolated from the gas to be measured includes, for example, a fuel electrode (hydrogen electrode) line piping of the fuel cell system.
[0053]
Also in this embodiment, either or both of the pressure P and the temperature T of the gas to be measured are separately measured, and the detected oxygen concentration is corrected according to the measured gas pressure P and / or gas temperature T. You may do it.
[0054]
The following third embodiment will be described.
FIG. 4 is a cross-sectional view of a sensor element of a gas sensor 300 according to the third embodiment of the present invention. Also in FIG. 4, the same parts as those in the first embodiment (FIG. 1) are denoted by the same reference numerals, and the description thereof is omitted. In this embodiment, the gas (O 2) of both the oxygen electrode line and the hydrogen electrode line of a fuel cell (not shown) is used. ₂ , H ₂ ) To be measured gas 1.
[0055]
In FIG. 4, the right support (corresponding to the upper support) 11 is formed with an oxygen electrode line 16 communicating with the oxygen electrode side of the fuel cell, and the left support (on the lower support). (Corresponding) 21 is formed with a hydrogen electrode line 26 communicating with the hydrogen electrode side of the fuel cell. In this embodiment, the second measured gas introduction hole (corresponding to the second diffusion rate controlling means) 22 that communicates with the hydrogen electrode line 26 is also connected to the first measured gas introduction hole (first measurement gas) that communicates with the oxygen electrode line 16. Like (1 diffusion rate limiting means) 12, it is formed to have a predetermined diffusion resistance (provide diffusion rate limiting).
[0056]
Further, unlike the first and second embodiments, the communication passage 15 is not provided, and each electrode (13a, 14a, 23a, 24a) is disposed in an isolated vacant space (reference number omitted), The third electrode 14a constitutes a reference electrode for the second electrode 23a, and the fourth electrode 24a constitutes a reference electrode for the first electrode 13a.
[0057]
Furthermore, the first hydrogen sensing circuit 31 for detecting the hydrogen partial pressure (concentration) on the first electrode 13a side is electrically connected between the first electrode 13a and the fourth electrode (reference electrode) 24a. In addition, a second hydrogen sensing circuit 32 that detects a hydrogen partial pressure (concentration) P2 on the second electrode 23a side is electrically connected between the second electrode 23a and the third electrode (reference electrode) 14a. . That is, in the present embodiment, the first hydrogen sensing circuit 31, the first electrode 13a, and the fourth electrode 24a correspond to the first hydrogen concentration detecting means according to the present invention, and the second hydrogen sensing circuit 32, the second electrode 23a, and The third electrode 14a corresponds to the second hydrogen concentration detecting means according to the present invention. In addition, the density | concentration on each electrode side has the same meaning as the density | concentration in the empty space where each electrode is arrange | positioned.
[0058]
Here, first, detection of the hydrogen concentration in the present embodiment will be described.
The amount of hydrogen that diffuses and flows into the second electrode 23 a side (in the second vacant chamber 23) through the second measured gas introduction hole 22 is equal to the hydrogen concentration C 1 ′ in the measured gas in the hydrogen electrode line 26 and the second concentration. Depending on the concentration difference from the hydrogen concentration C2 ′ on the electrode 23a side, the amount is limited. Accordingly, the hydrogen concentration C2 ′ on the second electrode 23a side is almost 0 (partial pressure conversion 10 ^-Ten The amount of hydrogen depending on the hydrogen concentration C1 ′ in the gas to be measured in the hydrogen electrode line 26 flows into the second electrode side 23a.
[0059]
Therefore, the hydrogen pumping circuit 40 is controlled so that the electromotive force (Vs−2) detected by the second hydrogen sensing circuit 32 becomes a value at which the hydrogen concentration on the second electrode 23a side becomes “almost 0”. The hydrogen pumping current (Ip-2) at this time can be expressed by the following equation (5).
[0060]
(Ip-2) = (nF / RT) .D.P.A / L. (C1'-C2 ') (5)
In the above equation (5), since the hydrogen concentration C2 ′ (≈0) on the second electrode 23a side, the measured hydrogen pumping current (Ip−2), that is, the amount of proton transported, the measured value in the hydrogen electrode line 26. The hydrogen concentration C1 ′ in the gas can be obtained.
[0061]
Next, detection of oxygen concentration will be described.
The detection of the oxygen concentration in the present embodiment is basically the same as in the first and second embodiments. That is, the electromotive force (Vs-1) detected by the first hydrogen sensing circuit 31 is set to a value at which the hydrogen concentration (= oxygen concentration) on the first electrode 13a side (in the first vacant chamber 13) becomes “almost 0”. Thus, the hydrogen pumping circuit 40 is controlled. The hydrogen pumping current (Ip-1) at this time can be expressed as the following equation (6), similarly to the above equation (3).
[0062]
(Ip-1) = 2 · nF / RT · D · P · A / L · (C1-C2) (6)
However, C1: oxygen concentration in the gas to be measured in the oxygen electrode line 16, C2: oxygen concentration on the first electrode 13a side (≈0)
Thereby, the oxygen concentration C1 in the gas under measurement in the oxygen electrode line 16 can be obtained from the detected hydrogen pumping current (Ip-1), that is, the proton transport amount.
[0063]
In the third embodiment, the hydrogen pumping circuit 40 is controlled based on the detection result of the first hydrogen sensing circuit 31 or the control result based on the detection result of the second hydrogen sensing circuit 32. One sensor can detect the oxygen concentration in the gas to be measured on the electrode line 16 side and the hydrogen concentration in the gas to be measured on the hydrogen electrode line 26 side.
[0064]
Further, the switching of the control is performed at a predetermined time interval (for example, an interval of about 1 second) set as necessary, or according to the necessity (request) in the fuel cell system. Good. As described above, the detection of the oxygen concentration on the oxygen electrode line 16 side and the detection of the hydrogen concentration on the hydrogen electrode line 16 side are switched every predetermined time or based on a command from the fuel cell system, so that it is important in the fuel cell system. The appropriate oxygen concentration and hydrogen concentration can be detected in sequence or as needed.
[0065]
Also in the present embodiment, either or both of the pressure and temperature of the gas in the oxygen electrode line 16 are separately measured and detected according to the measured gas pressure and / or gas temperature in the oxygen electrode line 16. Hydrogen which is detected in accordance with the measured gas pressure and / or gas temperature in the hydrogen electrode line 26 by correcting the oxygen concentration or separately measuring either or both of the pressure and temperature of the gas in the hydrogen electrode line 26 The density may be corrected.
[0066]
Next, a fourth embodiment will be described.
FIG. 5 shows a fourth embodiment of the present invention, and schematically shows a part in which an electrolyte body used as a fuel battery cell is diverted to a gas sensor. The proton conductive solid electrolyte body 10 used in the first to third embodiments is equivalent to an electrolyte body for a fuel battery cell. Therefore, this fuel battery cell electrolyte body is used as a proton conductor for a gas sensor. The conductive solid electrolyte body 10 can be used. Since the detection of the oxygen concentration, the detection of the hydrogen concentration, and the correction thereof are the same as those already described, the description thereof is omitted here.
[0067]
In FIG. 5, the gas sensor 400 is attached to the gas inlet portion 2a and the gas outlet portion 2b of a specific cell of the fuel cell (stack), but the gas sensor portion and the power generation portion of the fuel cell are electrically connected. In other words, it is possible to detect the gas concentration (oxygen concentration, hydrogen concentration) at an arbitrary site inside the cell.
[0068]
In the fourth embodiment, since a part of the proton conductive solid electrolyte body (for power generation) used for the fuel cell is used as the electrolyte body for the gas sensor, the gas concentration in the power generation electrolyte body can be directly detected. Highly responsive detection is possible. In addition, the cost can be reduced by sharing, and the oxygen concentration and hydrogen concentration at any position (gas inlet, gas outlet, inside the cell) of the fuel cell (stack) can be reduced by diverting part of the fuel cell. It can be detected.
[0069]
Furthermore, by disposing any of the gas sensors described above in the fuel gas line of the fuel cell system, the oxygen gas concentration and the hydrogen gas concentration, which are the main components of the fuel cell system, can be detected accurately, and from these gas concentration information By further optimizing the oxygen supply flow rate control and the hydrogen supply flow rate control, it is possible to improve the performance such as the operation efficiency and the followability at the time of transition. Moreover, since the gas sensor operates stably even at a low temperature, it is not necessary to provide an overheating means such as a heater, so the safety of the fuel cell system is not impaired and the configuration is simple. It can be realized at a relatively low cost.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of a gas sensor according to the present invention.
FIG. 2 is a graph showing the relationship between the hydrogen concentration (oxygen concentration) in the third vacancy 14 (= first vacancy 13) and the electromotive force.
FIG. 3 is a view showing a second embodiment of the gas sensor according to the present invention.
FIG. 4 is a diagram showing a third embodiment of a gas sensor according to the present invention.
FIG. 5 is a diagram showing a fourth embodiment of a gas sensor according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Proton conductive solid electrolyte body, 12, 22 ... Measuring gas introduction hole, 13 ... 1st empty room, 13a ... 1st electrode, 14 ... 3rd empty room, 14a ... 3rd electrode, 23 ... 2nd empty Chamber, 23a ... second electrode, 24 ... fourth empty chamber, 24a ... fourth electrode, 30,31,32 ... hydrogen sensing circuit, 40 ... hydrogen pumping circuit, 100,200,300,400 ... gas sensor

Claims

Diffusion rate limiting means for limiting the gas to be measured and allowing it to diffuse and flow into the measurement chamber;
Hydrogen transport means for transporting hydrogen separated from hydrogen-containing components to the measurement chamber;
An oxidation reaction means for reacting the transported hydrogen with oxygen in the measurement gas flowing into the measurement chamber;
Hydrogen concentration detection means for detecting the hydrogen concentration in the measurement chamber,
A gas sensor, wherein the amount of hydrogen transported to the measurement chamber is controlled so that the hydrogen concentration in the measurement chamber becomes a predetermined concentration, and the oxygen concentration in the measurement gas is detected based on the hydrogen transport amount.

The hydrogen transport means includes
A proton conductive solid electrolyte body;
A measurement chamber side electrode provided on the measurement chamber side of the proton conductive solid electrolyte body;
A hydrogen-containing component-side electrode provided on the hydrogen-containing component side on the opposite side of the proton conductive solid electrolyte body with respect to the measurement chamber-side electrode,
The proton is generated at the hydrogen-containing component side electrode by applying a predetermined voltage between both electrodes, and the generated proton is moved to the measurement chamber side electrode to transport hydrogen. Gas sensor.

The gas sensor according to claim 2, wherein the measurement chamber side electrode functions as an oxidation catalyst.

The hydrogen concentration detecting means includes
A proton conductive solid electrolyte body;
A measurement chamber side electrode provided on the measurement chamber side of the proton conductive solid electrolyte body;
A reference side electrode provided on the opposite side of the proton conductive solid electrolyte body with respect to the measurement chamber side electrode,
The gas sensor according to any one of claims 1 to 3, wherein a hydrogen concentration in the measurement chamber is detected based on an electromotive force generated between both electrodes.

The gas sensor according to any one of claims 1 to 4, wherein the hydrogen-containing component is water vapor in the gas to be measured.

The gas sensor according to any one of claims 1 to 4, wherein the hydrogen-containing component is water vapor in the atmosphere isolated from the gas to be measured.

The gas sensor according to any one of claims 1 to 4, wherein the hydrogen-containing component is hydrogen in a pipe isolated from the gas to be measured.

The gas sensor according to claim 1, wherein the detected oxygen concentration is corrected according to at least one of a temperature and a pressure of the gas to be measured.

First diffusion rate limiting means for restricting the gas to be measured on the oxygen electrode side of the fuel cell and diffusing and flowing into the first measurement chamber;
Second diffusion rate limiting means for restricting the gas to be measured on the hydrogen electrode side of the fuel cell and allowing the gas to diffuse and flow into the second measurement chamber;
Hydrogen transport means for transporting hydrogen from the second measurement chamber to the first measurement chamber;
An oxidation reaction means for reacting the transported hydrogen with oxygen in the measurement gas flowing into the first measurement chamber;
First hydrogen concentration detection means for detecting the hydrogen concentration in the first measurement chamber;
A second hydrogen concentration detecting means for detecting a hydrogen concentration in the second measurement chamber,
When the amount of hydrogen transported to the first measurement chamber is controlled so that the hydrogen concentration in the first measurement chamber becomes a predetermined concentration, the oxygen concentration in the gas to be measured on the oxygen electrode side based on this hydrogen transport amount While detecting
When the amount of hydrogen transported to the first measurement chamber is controlled so that the hydrogen concentration in the second measurement chamber becomes a predetermined concentration, the hydrogen concentration in the gas to be measured on the hydrogen electrode side based on this hydrogen transport amount A gas sensor characterized by detecting gas.

The gas sensor according to claim 9, wherein the detection of the oxygen concentration and the detection of the hydrogen concentration are switched at predetermined time intervals or based on a command from a fuel cell system.

The hydrogen transport means includes
A proton conductive solid electrolyte body;
A first electrode provided on the first measurement chamber side of the proton conductive solid electrolyte body;
A second electrode provided on the second measurement chamber side opposite to the proton conductive solid electrolyte body with respect to the first electrode,
11. A proton is generated at the second electrode by applying a predetermined voltage between both electrodes, and the generated proton is moved to the first electrode to transport hydrogen. The gas sensor described.

The gas sensor according to claim 11, wherein the first electrode has a function as an oxidation catalyst.

The first hydrogen concentration detecting means includes
A proton conductive solid electrolyte body;
A first electrode provided on the first measurement chamber side of the proton conductive solid electrolyte body;
A third electrode provided as a reference electrode on the opposite side of the proton conductive solid electrolyte body with respect to the first electrode,
The gas sensor according to any one of claims 9 to 12, wherein a hydrogen concentration in the first measurement chamber is detected based on an electromotive force generated between the first electrode and the third electrode. .

The second hydrogen concentration detecting means includes
A proton conductive solid electrolyte body;
A second electrode provided on the second measurement chamber side of the proton conductive solid electrolyte body;
A fourth electrode provided as a reference electrode on the opposite side of the proton conductive solid electrolyte body with respect to the second electrode,
The gas sensor according to any one of claims 9 to 13, wherein a hydrogen concentration in the second measurement chamber is detected based on an electromotive force generated between the second electrode and the fourth electrode. .

While correcting the detected oxygen concentration in the gas on the oxygen electrode side according to at least one of the temperature and pressure of the gas on the oxygen electrode side,
The hydrogen concentration in the detected gas on the hydrogen electrode side is corrected in accordance with at least one of the temperature and pressure of the gas on the hydrogen electrode side, according to any one of claims 9 to 14. The gas sensor described.

The proton-conductive solid electrolyte body is a part of a proton-conductive solid electrolyte body for a fuel cell, according to any one of claims 2 to 8, and 11 to 15. The gas sensor described.

A fuel cell system for generating electricity using a fuel cell,
A fuel cell system comprising the gas sensor according to any one of claims 1 to 16 in a fuel gas path.