JP3962583B2

JP3962583B2 - Electrochemical gas sensor

Info

Publication number: JP3962583B2
Application number: JP2001369565A
Authority: JP
Inventors: 仁中村; 順一小坂
Original assignee: Komyo Rikagaku Kogyo KK
Current assignee: Komyo Rikagaku Kogyo KK
Priority date: 2001-12-04
Filing date: 2001-12-04
Publication date: 2007-08-22
Anticipated expiration: 2021-12-04
Also published as: JP2003166971A

Description

【０００１】
【発明の属する技術分野】
本発明はガスセンサの技術分野にかかり、特に、水素ガス濃度を測定可能なガスセンサに関する。
【０００２】
【従来の技術】
図９、図１０の符号１０２は従来技術のガスセンサを示している。図１０は図９のＡ−Ａ線截断面図である。
【０００３】
このガスセンサ１０２は、全体が四角柱状の形状であり、容器本体１１５内には両端が開放された空洞１３０が設けられている。
【０００４】
この空洞１３０の両端は、空洞１３０内に電解液１１０が蓄えられた状態で、第１、第２の多孔質膜１１３、１１７を介して第１、第２の側板１１１、１１９によって塞がれている。
【０００５】
図中の符号１１４、１１６は第１、第２の多孔質膜１１３、１１７と容器本体１１５の間に配置されたパッキンであり、電解液１１０の漏出を防止している。
【０００６】
第１、第２の多孔質膜１１３、１１７の表面のうち、第１の多孔質膜１１３の電解液１１０と接する側の面には作用電極１３１が設けられており、第２の多孔質膜１１７の電解液１１０と接する側の面には、互いに離間した位置に、対電極１３２と比較電極１３３とが設けられている。
【０００７】
各電極１３１〜１３３にはリード線１３５〜１３７がそれぞれ取り付けられており、各電極１３１〜１３３を外部の測定回路に接続できるようになっている。
【０００８】
第１の側板１１１と第１の多孔質膜１１３との間には、ガス室１３８が設けられている。第１の側板１１１には、一端がガス室１３８に接続され、他端がガスセンサ１０２の周囲の空間に接続された２個の孔が穿設されており、一方の孔を吸気孔１２１とし、他方の孔を排気孔１２９とすると、ガスセンサ１０２が置かれた雰囲気中の気体を、吸気孔１２１からガス室１３８内に供給し、排気孔１２９から排気するようになっている。
【０００９】
ガス室１３８内の気体は第１の多孔質膜１１３を膜厚方向に浸透し、電解液１１０は第１の電極１３１を浸透し、第１の電極１３１と第１の多孔質膜１１３の界面に到達し、その界面近傍の第１の電極１３１内部で反応する。
【００１０】
例えば、ガス室１３８内に供給される分析対象ガス中に一酸化炭素が含まれた場合、第１の電極１３１と第１の多孔質膜１１３の界面近傍では、下記の反応が生じる。
ＣＯ＋Ｈ₂Ｏ → ＣＯ₂ ＋２Ｈ⁺ ＋２ｅ^- ……(１)
【００１１】
図中の符号１１２、１１８は、第１、第２の側板１１１、１１９と第１、第２の多孔質膜１１３、１１７との間に設けられたパッキンである。
【００１２】
第２の側板１１９と、該第２の側板１１９と第２の多孔質膜１１７の間に配置されたパッキン１１８には、空気孔１２７、１２６がそれぞれ穿設されており、電気化学式ガスセンサ１０２周囲の空気は、この空気孔１２７、１２６を通って第２の多孔質膜１１７の表面に供給されるようになっている。
【００１３】
供給された空気は第２の多孔質膜１１７を膜厚方向に浸透し、電解液１１０が浸透した対電極１３２に到達すると、第２の多孔質膜１１７と対電極１３２の界面近傍の対電極１３２の内部側の位置で下記の化学反応が生じる。
Ｏ₂／２＋２Ｈ⁺ ＋２ｅ^- → Ｈ₂Ｏ ……(２)
【００１４】
図８に示すように、オペアンプ１５１と基準電圧源１５２と抵抗１５３とを用意し、作用電極１３１を接地電位に接続し、対電極１３２を抵抗１５３の一端１５５に接続すると共に、オペアンプ１５１の反転入力端子と非反転入力端子と出力端子を、それぞれ比較電極１３３と基準電圧源１５２と抵抗１５３の他端１５６に接続すると、上記(１)、(２)式で生じた電荷に応じた大きさの電流が抵抗１５３に流れるため、抵抗１５３に生じる電圧降下の大きさを測定すると分析対象ガス中の特定のガス(ここではＣＯ)の濃度が分かるようになっている。
【００１５】
しかしながら上記のような測定方法では、検出対象の空気中に複数種類の気体が含まれる場合、全ての気体が第１の多孔質膜１１３を浸透するため、検出対象の気体の反応による電流の他、他の気体の反応による電流も測定してしまい、特定の気体だけの濃度を正確に求めることができない。特に、水素ガスを検出しようとすると、従来技術のガスセンサ１０２では空気中に含まれる一酸化炭素や硫化水素の影響を受けてしまうことが知られており、解決が望まれている。
【００１６】
【発明が解決しようとする課題】
本発明は上記従来技術の不都合を解決するために創作されたものであり、その目的は、サンプルガス中に含まれる特定のガス、特に水素ガスを検出できる電気化学式ガスセンサを提供することにある。
【００１７】
【課題を解決するための手段】
上記課題を解決するために、請求項１記載の発明は、多孔質膜と、前記多孔質膜表面に形成された作用電極と、前記作用電極と接触し、前記作用電極内に浸透可能な電解液とを有し、前記多孔質膜内を浸透した分析対象の気体が前記電解液と反応し、反応量に応じて前記作用電極に流れる電流を測定し、前記分析対象の気体の濃度を測定するように構成された電気化学式ガスセンサであって、前記多孔質膜の空隙率よりも小さい空隙率のフィルタ膜を有し、前記分析対象の気体は、前記フィルタ膜内部を前記フィルタ膜の表面に沿った方向に浸透して前記多孔質膜に到達した後、前記多孔質膜内部を前記多孔質膜の表面に沿った方向と膜厚方向に浸透し、前記電解液と反応するように構成された電気化学式ガスセンサである。
請求項２記載の発明は、多孔質膜と、前記多孔質膜表面に形成された作用電極と、前記作用電極と接触し、前記作用電極内に浸透可能な電解液とを有し、前記多孔質膜内を浸透した分析対象の気体が、前記電解液と反応し、反応量に応じて前記作用電極に流れる電流を測定し、前記分析対象の気体の濃度を測定するように構成された電気化学式ガスセンサであって、前記分析対象の気体は、前記多孔質膜の一部が圧縮されて構成されたフィルタ膜内部を、前記フィルタ膜の表面に沿った方向に浸透して前記多孔質膜に到達した後、前記多孔質膜内部を前記多孔質膜の表面に沿った方向と膜厚方向に浸透し、前記電解液と反応するように構成された電気化学式ガスセンサである。
請求項３記載の発明は、前記電解液と接触する対電極と比較電極とを有する請求項１又は請求項２のいずれか１項記載の電気化学式ガスセンサである。
請求項４記載の発明は、前記対電極と前記比較電極は、前記多孔質膜とは別の対電極側多孔質膜表面に形成され、該対電極側多孔質膜を通して前記電解液に酸素が供給されるように構成された請求項３記載の電気化学式ガスセンサである。
【００１８】
本発明の電気化学式ガスセンサは上記のように構成されており、電解液が作用電極を浸透し、気体が多孔質膜を浸透し、作用電極と多孔質膜の界面で電解液と気体が接触すると、作用電極と多孔質膜の界面である気液界面の近傍位置の作用電極内で反応が生じうる。
【００１９】
本発明では、気体が気液界面付近まで到達するためには、気体は多孔質膜よりも空隙率の小さいフィルタ膜の内部を膜表面と平行な方向に通過する必要があるため、分子が大きい気体は通過できず、検出対象ガスに含まれる水素ガスだけがフィルタ膜を通過し、気液界面に到達することができる。
【００２０】
一般に、多孔質膜の空隙率は５０％以上であるが、水素ガスだけを透過させるフィルタ膜の空隙率は４０％以下であることが望ましい。
【００２１】
このようなフィルタ膜は、空隙率５０％以上の多孔質膜を膜厚方向に圧縮して作製することができるが、非圧縮状態でも空隙率が４０％以下であればフィルタ膜として用いることができる。
【００２２】
【発明の実施の形態】
図２は本発明の電気化学式ガスセンサ２の正面図であり、図１は、その電気化学式ガスセンサ２の分解斜視図である。
【００２３】
この電気化学式ガスセンサ２は、作用電極側側板１１と、第１の圧縮部材１２と、作用電極側多孔質膜１３と、第２の圧縮部材１４と、容器本体１５と、第１のパッキンシールド１６と、対電極側多孔質膜１７と、第２のパッキンシールド１８と、対電極側側板１９とがこの順序で配置されている。
【００２４】
これらの部材１１〜１９は、作用電極側多孔質膜１３と対電極側多孔質膜１７とを除き、外形が矩形の板形状、又は正面矩形の直方体形状になっており、それら矩形の部材１１、１２、１４〜１６、１８、１９の四隅には、ねじ穴３９が設けられている。
【００２５】
容器本体１５には、空洞２４が設けられており、各部材１１〜１９は、図４に示すように、空洞２４内に電解液１０が充填された状態で、符号１１〜１９の順序で密着され、ねじ穴３９内にねじ４０がねじ込まれることで、互いに固定されている。ここでは電解液１０として、硫酸、リン酸等の酸、水酸化カリウム、水酸化ナトリウム等の塩基、又は塩化カリウム等の塩の水溶液が用いられる。
【００２６】
図４は、符号１１〜１５の間の部材、即ち作用電極側側板１１と容器本体１５の間は、Ａ−Ａ線截断面図に相当し、符号１６〜１９の間の部材、即ち第１のパッキン部材１６から対電極側側板１９の間はＢ−Ｂ線切断面図に相当する。
【００２７】
容器本体１５の平面図を図３に示す。空洞２４は、断面が円形の円筒部分４１と、断面が半円の半円筒部分４２とが接続されて構成されており、円筒部分４１の底は、段差が形成されており、容器本体１５の壁面である底面４４を除き、半円筒部分４２の上端部が位置している。
【００２８】
作用電極側多孔質膜１３及び対電極側多孔質膜１７には疎水性の材料が用いられ、その表面及び内部には細孔が多数形成されている。この細孔の直径は、気体分子の平均自由行程よりも大きな５０Å〜１μｍ程度の大きさであり、気体に対しては透過性を有するが、水溶液に対しては透過性を有さない。
【００２９】
ここで、作用電極側多孔質膜１３や対電極側多孔質膜１７は、通常、多孔質の四フッ化エチレン膜によって構成されており、その細孔の含有率、即ち空隙率Ｖ₁は、５０％以上８０％以下の大きさである。
【００３０】
ねじ穴３９内のねじ４０を所定トルクで締め付け、各部材１１〜１９を密着させた状態でねじ止め固定すると、作用電極側多孔質膜１３のうち、第１、第２の圧縮部材１２、１４によって挟まれた部分が容器本体１５と作用電極側側板１１との間で押圧され、膜厚方向に圧縮されて厚みが薄くなる。
【００３１】
他方、作用電極側多孔質膜１３の半円筒部分４２に面する部分は、片側が電解液１０と接触しているため押圧されない。
【００３２】
図５は、図４の符号ａで示した部分の拡大図であり、図５の符号１３Ａは作用電極側多孔質膜１３の圧縮された部分から成るフィルタ膜を示している。このフィルタ膜１３Ａの空隙率Ｖ₂は、組立前の作用電極側多孔質膜１３の空隙率Ｖ₁よりも小さく、４０％以下の大きさである。空隙率Ｖ₁の下限は、水素ガスが透過でき、ガスセンサとしての応答性が低下しない程度の大きさが必要であり、５％以上の大きさが必要であると予想される。
【００３３】
他方、作用電極側多孔質膜１３のうち、空洞２４の半円筒部分４１に当たる箇所は圧縮されず、厚みに変化はない。図５の符号１３Ｂは厚みの変化のない部分である非圧縮多孔質膜を示している。この非圧縮多孔質膜１３Ｂの空隙率Ｖ₃は、組立前の作用電極側多孔質膜１３の空隙率Ｖ₁に等しい。
【００３４】
作用電極側側板１１及び対電極側側板１９は樹脂製であり、厚み方向に貫通する細孔により、ガス供給路２０と空気供給路２７とがそれぞれ形成されている。
【００３５】
第１、第２の圧縮部材１２、１４と、第１、第２のパッキンシールド１６、１８は、ゴム等の弾性部材製の膜であり、作用電極側側板１１と接触する第１の圧縮部材１２と、対電極側側板１９と接触する第２のパッキンシールド１８には、ガス供給路２０と連通する位置と、空気供給路２７と連通する位置に、それぞれ孔２１、２６が形成されている。
【００３６】
ガス供給路２０と空気供給路２７は、作用電極側側板１１の外部表面と対電極側側板１９の外部表面にそれぞれ開口を有しており、ガス供給路２０と空気供給路２７に供給された気体は、各開口からガス供給路２０と空気供給路２７とを通り、孔２１、２６を介して電気化学式ガスセンサ２の内部に導かれるようになっている。
【００３７】
この空気供給路２７は酸素ガスの供給が目的であり、酸素ガス以外の他の反応性ガスが供給されると、後述する比較電極３２の電位に影響を与えてしまうため、通常、パッキン１８と対電極側多孔質膜１７の間に、他の反応性ガスが透過せず、酸素ガスが透過可能な選択性フィルタ膜を設ける場合が多い。
【００３８】
第１の圧縮部材１２に形成された孔２１は、作用電極側多孔質膜１３の圧縮された部分であるフィルタ膜１３Ａ上に位置しており、ガス供給路２０を通ったサンプルガスはフィルタ膜１３Ａと接触する。図１、図４、図５の符号３０は、ガス供給路２０を通ったサンプルガスが接触するフィルタ膜１３Ａ上の位置、即ちサンプルガスの接触位置を示している。
【００３９】
フィルタ膜１３Ａは、接触位置３０以外の部分では気体と接触しないようになっており、フィルタ膜１３Ａの接触位置３０以外の表面は第１の圧縮部材１２と密着し、裏面側は全面的に第２の圧縮部材１４に密着している。
【００４０】
接触位置３０においてフィルタ膜１３Ａと接触したサンプルガスは、フィルタ膜１３Ａの内部をフィルタ膜１３Ａの膜厚方向に浸透し得るが、フィルタ膜１３Ａの空隙率Ｖ₂は小さいため水素ガス以外のガスは実質的に浸透することができない。
【００４１】
従って、ガス供給路２０を通り、接触位置３０においてフィルタ膜１３Ａと接触したサンプルガス中に水素ガスが含まれていた場合、水素ガスだけがフィルタ膜１３Ａ内を浸透し、圧縮されていない状態の非圧縮多孔質膜１３Ｂに到達する。
【００４２】
ここでは孔２１は円形であり、接触位置３０の中心から非圧縮多孔質膜１３Ｂの端部までの長さ、即ち水素ガスがフィルタ膜１３Ａ内を浸透する距離は、１ｍｍ以上の長さが必要であり、３ｍｍ以上１０ｍｍ以下の範囲が望ましい。
【００４３】
非圧縮多孔質膜１３Ｂの表面には、作用電極３１が形成されている。この作用電極３１は、半円筒部分４１の底面に位置しており、電解液１０と接触している。
【００４４】
作用電極３１及び後述する対電極３２と比較電極３３とは、白金や金から成り、多孔質になっている。
【００４５】
電解液１０は作用電極３１の内部をその膜厚方向に浸透していて、非圧縮多孔質膜１３Ｂと作用電極３１の界面付近にまで到達している。
【００４６】
フィルタ膜１３Ａの内部をその膜表面と平行な方向に浸透した水素ガスは、非圧縮多孔質膜１３Ｂ到達すると、非圧縮多孔質膜１３Ｂの膜表面と平行な方向と膜厚方向に浸透し、作用電極３１と非圧縮多孔質膜１３Ｂの界面付近にまで到達すると、作用電極３１内に浸透している電解液１０と下記のように反応し、作用電極３１に電子を供給する。
Ｈ₂ → ２Ｈ⁺ ＋２ｅ^- ……(３)
【００４７】
他方、対電極側多孔質膜１７の電解液１０と接触する側の表面には、対電極３２と比較電極３３とが互いに非接触な状態で配置されている。
【００４８】
上述の空気供給孔２７と孔２６を通って供給された酸素ガスは、対電極側多孔質膜１７と接触し、対電極側多孔質膜１７を膜厚方向に浸透し、対電極３２と対電極側多孔質膜１７との界面の近傍位置の対電極３２の内部で、酸素ガスと、対電極３２から供給される電子と、電解液１０から供給される水素イオンとの間で下記のような反応が生じる。
Ｏ₂／２＋２Ｈ⁺ ＋２ｅ^- → Ｈ₂Ｏ ……(４)
【００４９】
作用電極３１と対電極３２と比較電極３３には、それぞれリード線３５〜３７が接続されており、電気化学式ガスセンサ２は、図６に示した測定回路に接続される。この図６の測定回路は、図８に示した測定回路と同じであり、オペアンプ５１と基準電圧源５２と抵抗５３とを有している。作用電極３１は接地電位に接続され、対電極３２は、抵抗５３の一端５５に接続されている。
【００５０】
オペアンプ５１の反転入力端子と非反転入力端子と出力端子は、それぞれ比較電極３３と、基準電圧源５２と、抵抗５３の他端５６に接続されている。
【００５１】
サンプルガス中に水素ガスが含まれていると、上記(３)式で生じた電子が作用電極３１に放出されると共に水素イオンが電解液１０中に放出される。対電極３２側では回路側から対電極３２に電子が供給され、電解液１０側から水素イオンが供給されるため、対電極３２の内部で上記(４)式の反応が生じる。
【００５２】
これらの反応によって生じた電流は抵抗５２を流れ、その両端の電圧が出力電圧となってサンプルガス中の水素ガス濃度が検出される。
【００５３】
下記表は、本発明の電気化学式ガスセンサと、従来技術の電気化学式ガスセンサの検出感度を図６、図８の測定回路を使用して比較した実験結果である。
【００５４】
使用した多孔質膜１３は、膜厚０．５４ｍｍ、空隙率が５４％の四フッ化エチレン樹脂から成る膜であり、その多孔質膜１３の膜厚を１／２に圧縮し、空隙率が２７％のフィルタ膜１３Ａを構成した。
【００５５】
【表１】

【００５６】
上記表１から分かるように、本発明の電気化学式ガスセンサ２は、水素ガスだけに感度を有しているのに対し、従来技術の電気化学式ガスセンサは、他のガスに対しても感度を有しており、水素ガスセンサとして用いることはできないことが分かる。
【００５７】
上記は、１枚の作用電極側多孔質膜１３を部分的に圧縮してフィルタ膜１３Ａを形成し、電気化学式ガスセンサ２を構成させた例について説明したが、本発明は、圧縮によって形成されたフィルタ膜に限定されるものではなく、予め多孔質膜の空隙率よりも小さい空隙率を有する樹脂フィルムを用意し、それを多孔質膜に接続して作用電極側多孔質膜を形成した電気化学式ガスセンサも含まれる。
【００５８】
その例を説明すると、図７の符号５３Ａ、５３Ｂは、四フッ化エチレン膜から成るフィルタ膜と多孔質膜とを示している。
【００５９】
このフィルタ膜５３Ａは、非圧縮の状態での空隙率が多孔質膜５３Ｂよりも小さくなっており、その端面が多孔質膜５３Ｂの端面に密着され、作用電極側多孔質膜５３が構成されている。
【００６０】
この作用電極側多孔質膜５３でも、その表面の接触位置３０において水素ガスがフィルタ膜５３Ａ内に浸透し、フィルタ膜５３Ａの内部を膜表面と平行な方向に拡散し、多孔質膜５３Ｂに到達し、作用電極３１内で反応する。
【００６１】
要するに、本発明に用いられるフィルタ膜は、圧縮することで空隙率を小さくした膜に限定されるものではなく、圧縮しない状態で多孔質膜よりも空隙率が小さい膜も含まれる。
【００６２】
なお、上記各実施例では、作用電極３１の他、対電極３２や比較電極３３を用いたが、本発明は電解液中で(３)式、(４)式の反応が進行すればよく、必ずしも比較電極３３は必要ではない。
【００６３】
【発明の効果】
特定の種類のガス、特に水素ガスの検出感度が高く、水素ガス以外の検出感度が低い電気化学式ガスセンサが得られる。
【図面の簡単な説明】
【図１】本発明の一例の電気化学式ガスセンサの分解斜視図
【図２】その組立状態の平面図
【図３】容器本体の平面図
【図４】図１のＡ−Ａ線又はＢ−Ｂ線截断面図
【図５】その電気化学式ガスセンサの部分拡大図
【図６】本発明の電気化学式ガスセンサが用いられる測定回路を説明するための回路ブロック図
【図７】本発明の他の例の電気化学式ガスセンサの部分拡大図
【図８】従来技術の電気化学式ガスセンサが用いられる測定回路の例
【図９】従来技術の電気化学式ガスセンサの平面図
【図１０】そのＡ−Ａ截断面図
【符号の説明】
２……電気化学式ガスセンサ
１０……電解液
１３Ａ……フィルタ膜
１３、１３Ｂ……多孔質膜
１７……対電極側多孔質膜
３１……作用電極
３２……対電極
３３……比較電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the technical field of gas sensors, and more particularly to a gas sensor capable of measuring a hydrogen gas concentration.
[0002]
[Prior art]
Reference numerals 102 in FIGS. 9 and 10 denote a conventional gas sensor. FIG. 10 is a cross-sectional view taken along line AA in FIG.
[0003]
The gas sensor 102 has a quadrangular prism shape as a whole, and a cavity 130 having both ends opened is provided in the container body 115.
[0004]
Both ends of the cavity 130 are closed by the first and

second side plates

111 and 119 via the first and second

porous films

113 and 117 in a state where the electrolyte solution 110 is stored in the cavity 130. ing.
[0005]

Reference numerals

114 and 116 in the figure denote packings disposed between the first and second

porous membranes

113 and 117 and the container main body 115 to prevent leakage of the electrolyte solution 110.
[0006]
Of the surfaces of the first and second

porous membranes

113 and 117, a working electrode 131 is provided on the surface of the first porous membrane 113 on the side in contact with the electrolytic solution 110, and the second porous membrane is provided. A counter electrode 132 and a comparative electrode 133 are provided on the surface of the 117 in contact with the electrolytic solution 110 at positions separated from each other.
[0007]
Lead wires 135 to 137 are respectively attached to the electrodes 131 to 133 so that the electrodes 131 to 133 can be connected to an external measurement circuit.
[0008]
A gas chamber 138 is provided between the first side plate 111 and the first porous film 113. The first side plate 111 has two holes, one end of which is connected to the gas chamber 138 and the other end connected to the space around the gas sensor 102. One of the holes is an intake hole 121. When the other hole is an exhaust hole 129, the gas in the atmosphere where the gas sensor 102 is placed is supplied from the intake hole 121 into the gas chamber 138 and exhausted from the exhaust hole 129.
[0009]
The gas in the gas chamber 138 penetrates the first porous film 113 in the film thickness direction, and the electrolytic solution 110 penetrates the first electrode 131, and the interface between the first electrode 131 and the first porous film 113. To react inside the first electrode 131 in the vicinity of the interface.
[0010]
For example, when carbon monoxide is contained in the analysis target gas supplied into the gas chamber 138, the following reaction occurs in the vicinity of the interface between the first electrode 131 and the first porous film 113.
CO + H ₂ O → CO ₂ + 2H ⁺ + 2e ⁻ (1)
[0011]

Reference numerals

112 and 118 in the figure denote packings provided between the first and

second side plates

111 and 119 and the first and second

porous films

113 and 117.
[0012]

Air holes

127 and 126 are formed in the second side plate 119 and the packing 118 disposed between the second side plate 119 and the second porous membrane 117, respectively. The air is supplied to the surface of the second porous membrane 117 through the

air holes

127 and 126.
[0013]
When the supplied air penetrates the second porous membrane 117 in the film thickness direction and reaches the counter electrode 132 into which the electrolytic solution 110 has penetrated, the counter electrode near the interface between the second porous membrane 117 and the counter electrode 132 is used. The following chemical reaction occurs at a position inside 132.
_{^{O 2/2 + 2H + +}} 2e - → H 2 O ...... (2)
[0014]
As shown in FIG. 8, an operational amplifier 151, a reference voltage source 152, and a resistor 153 are prepared, the working electrode 131 is connected to the ground potential, the counter electrode 132 is connected to one end 155 of the resistor 153, and the operational amplifier 151 is inverted. When the input terminal, the non-inverting input terminal, and the output terminal are connected to the comparison electrode 133, the reference voltage source 152, and the other end 156 of the resistor 153, respectively, the magnitude according to the electric charges generated in the above expressions (1) and (2). Therefore, the concentration of a specific gas (in this case, CO) in the analysis target gas can be determined by measuring the magnitude of the voltage drop generated in the resistor 153.
[0015]
However, in the measurement method as described above, when a plurality of types of gases are contained in the air to be detected, all the gases permeate the first porous film 113, so that in addition to the current due to the reaction of the gas to be detected The current due to the reaction of other gases is also measured, and the concentration of only a specific gas cannot be obtained accurately. In particular, when trying to detect hydrogen gas, it is known that the conventional gas sensor 102 is affected by carbon monoxide and hydrogen sulfide contained in the air, and a solution is desired.
[0016]
[Problems to be solved by the invention]
The present invention was created to solve the above-described disadvantages of the prior art, and an object thereof is to provide an electrochemical gas sensor capable of detecting a specific gas contained in a sample gas, particularly hydrogen gas.
[0017]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is directed to a porous membrane, a working electrode formed on the surface of the porous membrane, and an electrolysis that is in contact with the working electrode and can penetrate into the working electrode. A gas to be analyzed that has permeated through the porous membrane reacts with the electrolyte solution, measures the current flowing through the working electrode according to the reaction amount, and measures the concentration of the gas to be analyzed An electrochemical gas sensor configured to have a filter film having a porosity smaller than the porosity of the porous film, and the gas to be analyzed is placed inside the filter film on the surface of the filter film. It is configured to permeate in the direction along the surface and reach the porous film, then penetrates the inside of the porous film in the direction along the surface of the porous film and the film thickness direction, and reacts with the electrolytic solution. Electrochemical gas sensor.
The invention according to claim 2 comprises a porous membrane, a working electrode formed on the surface of the porous membrane, and an electrolyte solution that contacts the working electrode and can permeate into the working electrode. An electric gas configured to measure the concentration of the gas to be analyzed by measuring the current flowing through the working electrode according to the reaction amount when the gas to be analyzed that permeates through the membrane reacts with the electrolyte. In the chemical gas sensor, the gas to be analyzed penetrates through the inside of the filter membrane formed by compressing a part of the porous membrane in a direction along the surface of the filter membrane and enters the porous membrane. It is an electrochemical gas sensor configured to penetrate the inside of the porous membrane in the direction along the surface of the porous membrane and the film thickness direction after reaching and react with the electrolytic solution .
A third aspect of the present invention is the electrochemical gas sensor according to the first aspect or the second aspect of the present invention, comprising a counter electrode and a reference electrode that are in contact with the electrolytic solution.
According to a fourth aspect of the present invention, the counter electrode and the comparison electrode are formed on the surface of the counter electrode side porous film different from the porous film, and oxygen is supplied to the electrolyte solution through the counter electrode side porous film. The electrochemical gas sensor according to claim 3, wherein the electrochemical gas sensor is configured to be supplied.
[0018]
The electrochemical gas sensor of the present invention is configured as described above. When the electrolytic solution penetrates the working electrode, the gas penetrates the porous membrane, and the electrolytic solution and the gas contact at the interface between the working electrode and the porous membrane. A reaction can occur in the working electrode in the vicinity of the gas-liquid interface, which is the interface between the working electrode and the porous membrane.
[0019]
In the present invention, in order for the gas to reach the vicinity of the gas-liquid interface, the gas needs to pass through the inside of the filter membrane having a smaller porosity than the porous membrane in a direction parallel to the membrane surface, so that the molecules are large. Gas cannot pass through, and only hydrogen gas contained in the detection target gas can pass through the filter membrane and reach the gas-liquid interface.
[0020]
In general, the porosity of the porous membrane is 50% or more, but the porosity of the filter membrane that allows only hydrogen gas to pass through is desirably 40% or less.
[0021]
Such a filter membrane can be produced by compressing a porous membrane having a porosity of 50% or more in the film thickness direction, but can be used as a filter membrane if the porosity is 40% or less even in an uncompressed state. it can.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a front view of the electrochemical gas sensor 2 of the present invention, and FIG. 1 is an exploded perspective view of the electrochemical gas sensor 2.
[0023]
The electrochemical gas sensor 2 includes a working electrode side plate 11, a first compression member 12, a working electrode side porous membrane 13, a second compression member 14, a container body 15, and a first packing shield 16. The counter electrode side porous membrane 17, the second packing shield 18, and the counter electrode side plate 19 are arranged in this order.
[0024]
Except for the working electrode side porous membrane 13 and the counter electrode side porous membrane 17, these members 11 to 19 have a rectangular plate shape or a rectangular parallelepiped shape with a front rectangular shape. , 12, 14-16, 18, 19 are provided with screw holes 39 at the four corners.
[0025]
The container body 15 is provided with a cavity 24, and the members 11 to 19 are in close contact with each other in the order of reference numerals 11 to 19 with the electrolyte solution 10 filled in the cavity 24 as shown in FIG. Then, the screws 40 are screwed into the screw holes 39 to be fixed to each other. Here, as the electrolytic solution 10, an acid such as sulfuric acid or phosphoric acid, a base such as potassium hydroxide or sodium hydroxide, or an aqueous solution of a salt such as potassium chloride is used.
[0026]
4 corresponds to a cross-sectional view taken along the line AA between the working electrode side plate 11 and the container body 15, and the member between 16 and 19, i.e., the first member. A portion between the packing member 16 and the counter electrode side plate 19 corresponds to a sectional view taken along line B-B.
[0027]
A plan view of the container body 15 is shown in FIG. The cavity 24 is configured by connecting a cylindrical portion 41 having a circular cross section and a semicylindrical portion 42 having a semicircular cross section, and a step is formed at the bottom of the cylindrical portion 41, Except for the bottom surface 44 which is a wall surface, the upper end portion of the semi-cylindrical portion 42 is located.
[0028]
A hydrophobic material is used for the working electrode side porous film 13 and the counter electrode side porous film 17, and a large number of pores are formed on the surface and inside thereof. The diameter of the pore is about 50 μm to 1 μm larger than the mean free path of gas molecules, and is permeable to gas but not permeable to aqueous solution.
[0029]
Here, the working electrode side porous membrane 13 and the counter electrode side porous membrane 17 are usually composed of a porous tetrafluoroethylene membrane, and the pore content, that is, the porosity V ₁ is The size is 50% or more and 80% or less.
[0030]
When the screw 40 in the screw hole 39 is tightened with a predetermined torque and screwed and fixed in a state where the members 11 to 19 are brought into close contact with each other, the first and

second compression members

12 and 14 of the working electrode side porous membrane 13 are used. The portion sandwiched between the container body 15 and the working electrode side plate 11 is pressed and compressed in the film thickness direction to reduce the thickness.
[0031]
On the other hand, the portion facing the semi-cylindrical portion 42 of the working electrode side porous membrane 13 is not pressed because one side is in contact with the electrolytic solution 10.
[0032]
FIG. 5 is an enlarged view of the portion indicated by reference numeral a in FIG. 4, and reference numeral 13 </ b> A in FIG. 5 indicates a filter membrane composed of a compressed portion of the working electrode side porous membrane 13. The porosity V ₂ of the filter membrane 13A is smaller than the porosity V ₁ of the working electrode side porous membrane 13 before assembly and is 40% or less. The lower limit of the porosity V ₁ needs to be large enough to allow hydrogen gas to pass therethrough and not deteriorate the responsiveness as a gas sensor, and is expected to be 5% or more.
[0033]
On the other hand, in the working electrode side porous membrane 13, the portion corresponding to the semicylindrical portion 41 of the cavity 24 is not compressed and the thickness does not change. The code | symbol 13B of FIG. 5 has shown the non-compressed porous film | membrane which is a part with no thickness change. The porosity V ₃ of the non-compressed porous membrane 13B is equal to the porosity V ₁ of the working electrode side porous membrane 13 before assembly.
[0034]
The working electrode side plate 11 and the counter electrode side plate 19 are made of resin, and a gas supply path 20 and an air supply path 27 are formed by pores penetrating in the thickness direction.
[0035]
The first and

second compression members

12 and 14 and the first and second packing shields 16 and 18 are films made of an elastic member such as rubber, and are in contact with the working electrode side plate 11. 12 and the second packing shield 18 in contact with the counter electrode side plate 19 are formed with

holes

21 and 26 at a position communicating with the gas supply path 20 and a position communicating with the air supply path 27, respectively. .
[0036]
The gas supply path 20 and the air supply path 27 have openings on the outer surface of the working electrode side plate 11 and the outer surface of the counter electrode side plate 19, respectively, and are supplied to the gas supply path 20 and the air supply path 27. The gas passes through the gas supply path 20 and the air supply path 27 from each opening, and is introduced into the electrochemical gas sensor 2 through the

holes

21 and 26.
[0037]
This air supply path 27 is for the purpose of supplying oxygen gas, and if a reactive gas other than oxygen gas is supplied, it will affect the potential of the comparison electrode 32 described later. In many cases, a selective filter membrane that does not allow other reactive gas to permeate and allows oxygen gas to pass therethrough is provided between the counter electrode side porous membrane 17.
[0038]
The holes 21 formed in the first compression member 12 are located on the filter membrane 13A, which is a compressed portion of the working electrode side porous membrane 13, and the sample gas that has passed through the gas supply path 20 passes through the filter membrane. Contact 13A. 1, 4, and 5 indicate a position on the filter membrane 13 </ b> A where the sample gas that has passed through the gas supply path 20 comes into contact, that is, a contact position of the sample gas.
[0039]
The filter film 13A is configured not to come into contact with gas at a portion other than the contact position 30. The surface of the filter film 13A other than the contact position 30 is in close contact with the first compression member 12, and the back surface side is entirely the first. The two compression members 14 are in close contact with each other.
[0040]
Sample gas in contact with the filter membrane 13A at the contact position 30 is can penetrate the interior of the filter layer 13A in a thickness direction of the filter film 13A, the gas other than hydrogen gas for porosity V ₂ is smaller filter membrane 13A is Cannot penetrate substantially.
[0041]
Therefore, when hydrogen gas is contained in the sample gas that has passed through the gas supply path 20 and has contacted the filter membrane 13A at the contact position 30, only hydrogen gas permeates the filter membrane 13A and is not compressed. It reaches the incompressible porous membrane 13B.
[0042]
Here, the hole 21 is circular, and the length from the center of the contact position 30 to the end of the non-compressed porous membrane 13B, that is, the distance that hydrogen gas permeates through the filter membrane 13A needs to be 1 mm or longer. The range of 3 mm or more and 10 mm or less is desirable.
[0043]
A working electrode 31 is formed on the surface of the incompressible porous membrane 13B. The working electrode 31 is located on the bottom surface of the semi-cylindrical portion 41 and is in contact with the electrolytic solution 10.
[0044]
The working electrode 31 and a counter electrode 32 and a reference electrode 33 described later are made of platinum or gold and are porous.
[0045]
The electrolytic solution 10 penetrates the inside of the working electrode 31 in the film thickness direction and reaches the vicinity of the interface between the incompressible porous membrane 13B and the working electrode 31.
[0046]
When the hydrogen gas that has permeated the inside of the filter membrane 13A in the direction parallel to the membrane surface reaches the incompressible porous membrane 13B, it penetrates in the direction parallel to the membrane surface of the incompressible porous membrane 13B and the film thickness direction, When it reaches the vicinity of the interface between the working electrode 31 and the non-compressed porous membrane 13B, it reacts with the electrolytic solution 10 penetrating into the working electrode 31 as follows, and supplies electrons to the working electrode 31.
H ₂ → 2H ⁺ + 2e ⁻ (3)
[0047]
On the other hand, the counter electrode 32 and the comparison electrode 33 are disposed in a non-contact state on the surface of the counter electrode side porous membrane 17 on the side in contact with the electrolyte solution 10.
[0048]
The oxygen gas supplied through the air supply hole 27 and the hole 26 mentioned above comes into contact with the counter electrode-side porous film 17 and permeates the counter electrode-side porous film 17 in the film thickness direction. Inside the counter electrode 32 in the vicinity of the interface with the electrode-side porous membrane 17, the oxygen gas, the electrons supplied from the counter electrode 32, and the hydrogen ions supplied from the electrolytic solution 10 are as follows: Reaction occurs.
_{^{O 2/2 + 2H + +}} 2e - → H 2 O ...... (4)
[0049]
Lead wires 35 to 37 are connected to the working electrode 31, the counter electrode 32, and the comparison electrode 33, respectively, and the electrochemical gas sensor 2 is connected to the measuring circuit shown in FIG. The measurement circuit in FIG. 6 is the same as the measurement circuit shown in FIG. 8 and includes an operational amplifier 51, a reference voltage source 52, and a resistor 53. The working electrode 31 is connected to the ground potential, and the counter electrode 32 is connected to one end 55 of the resistor 53.
[0050]
The inverting input terminal, the non-inverting input terminal, and the output terminal of the operational amplifier 51 are connected to the comparison electrode 33, the reference voltage source 52, and the other end 56 of the resistor 53, respectively.
[0051]
When hydrogen gas is contained in the sample gas, electrons generated by the above equation (3) are released to the working electrode 31 and hydrogen ions are released into the electrolytic solution 10. On the counter electrode 32 side, electrons are supplied from the circuit side to the counter electrode 32 and hydrogen ions are supplied from the electrolyte solution 10 side, so that the reaction of the above formula (4) occurs inside the counter electrode 32.
[0052]
The current generated by these reactions flows through the resistor 52, and the voltage at both ends thereof becomes the output voltage to detect the hydrogen gas concentration in the sample gas.
[0053]
The following table shows the experimental results comparing the detection sensitivities of the electrochemical gas sensor of the present invention and the conventional electrochemical gas sensor using the measurement circuit of FIGS.
[0054]
The used porous membrane 13 is a membrane made of a tetrafluoroethylene resin having a thickness of 0.54 mm and a porosity of 54%. The thickness of the porous membrane 13 is compressed to ½, and the porosity is A 27% filter membrane 13A was constructed.
[0055]
[Table 1]

[0056]
As can be seen from Table 1 above, the electrochemical gas sensor 2 of the present invention is sensitive only to hydrogen gas, whereas the conventional electrochemical gas sensor is sensitive to other gases. It can be seen that it cannot be used as a hydrogen gas sensor.
[0057]
The above has described an example in which one working electrode side porous membrane 13 is partially compressed to form the filter membrane 13A to constitute the electrochemical gas sensor 2, but the present invention was formed by compression. It is not limited to the filter membrane, prepared in advance a resin film having a porosity smaller than the porosity of the porous membrane, and connected to the porous membrane to form a working electrode side porous membrane A gas sensor is also included.
[0058]
For example, reference numerals 53A and 53B in FIG. 7 indicate a filter film made of an ethylene tetrafluoride film and a porous film.
[0059]
The filter membrane 53A has a porosity in an uncompressed state smaller than that of the porous membrane 53B, and its end surface is in close contact with the end surface of the porous membrane 53B, thereby forming the working electrode side porous membrane 53. Yes.
[0060]
Also in this working electrode side porous membrane 53, hydrogen gas permeates into the filter membrane 53A at the contact position 30 on the surface , diffuses inside the filter membrane 53A in a direction parallel to the membrane surface, and reaches the porous membrane 53B. And react in the working electrode 31.
[0061]
In short, the filter membrane used in the present invention is not limited to a membrane having a reduced porosity by being compressed, and includes a membrane having a porosity lower than that of a porous membrane without being compressed.
[0062]
In each of the above examples, the counter electrode 32 and the comparative electrode 33 are used in addition to the working electrode 31. However, the present invention only requires that the reactions of the formulas (3) and (4) proceed in the electrolytic solution, The comparison electrode 33 is not necessarily required.
[0063]
【The invention's effect】
An electrochemical gas sensor having high detection sensitivity for a specific type of gas, particularly hydrogen gas, and low detection sensitivity other than hydrogen gas can be obtained.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an example of an electrochemical gas sensor according to the present invention. FIG. 2 is a plan view of an assembled state. FIG. 3 is a plan view of a container body. FIG. 5 is a partial enlarged view of the electrochemical gas sensor. FIG. 6 is a circuit block diagram for explaining a measurement circuit in which the electrochemical gas sensor of the present invention is used. FIG. 8 is an example of a measurement circuit in which a conventional electrochemical gas sensor is used. FIG. 9 is a plan view of a conventional electrochemical gas sensor. FIG. 10 is a cross-sectional view taken along line AA. Explanation of]
2 ... Electrochemical gas sensor 10 ... Electrolytic solution 13A ...

Filter membrane

13, 13B ... Porous membrane 17 ... Counter electrode-side porous membrane 31 ... Working electrode 32 ... Counter electrode 33 ... Comparative electrode

Claims

A porous membrane;
A working electrode formed on the surface of the porous membrane;
An electrolyte solution in contact with the working electrode and penetrating into the working electrode;
The gas to be analyzed that has penetrated through the porous membrane reacts with the electrolytic solution, and the current flowing through the working electrode is measured according to the reaction amount, and the concentration of the gas to be analyzed is measured. An electrochemical gas sensor,
Having a filter membrane with a porosity smaller than the porosity of the porous membrane,
The gas to be analyzed permeates the inside of the filter membrane in the direction along the surface of the filter membrane and reaches the porous membrane, and then the inside of the porous membrane passes in the direction along the surface of the porous membrane. An electrochemical gas sensor configured to penetrate in the film thickness direction and react with the electrolyte .

A porous membrane;
A working electrode formed on the surface of the porous membrane;
An electrolyte solution in contact with the working electrode and penetrating into the working electrode;
The gas to be analyzed that has penetrated through the porous membrane reacts with the electrolytic solution, and the current flowing through the working electrode is measured according to the reaction amount, and the concentration of the gas to be analyzed is measured. An electrochemical gas sensor,
The gas to be analyzed penetrates through the inside of the filter membrane formed by compressing a part of the porous membrane in the direction along the surface of the filter membrane, and reaches the porous membrane. An electrochemical gas sensor configured to permeate the inside of the membrane in the direction along the surface of the porous membrane and the thickness direction and react with the electrolytic solution .

The electrochemical gas sensor according to claim 1, further comprising a counter electrode and a reference electrode that are in contact with the electrolytic solution.

The counter electrode and the comparative electrode are formed on the surface of the counter electrode side porous membrane different from the porous membrane,
The electrochemical gas sensor according to claim 3, wherein oxygen is supplied to the electrolyte solution through the counter electrode-side porous membrane.