EP1934590A1 - Gas sensor - Google Patents

Gas sensor

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Publication number
EP1934590A1
EP1934590A1 EP06806778A EP06806778A EP1934590A1 EP 1934590 A1 EP1934590 A1 EP 1934590A1 EP 06806778 A EP06806778 A EP 06806778A EP 06806778 A EP06806778 A EP 06806778A EP 1934590 A1 EP1934590 A1 EP 1934590A1
Authority
EP
European Patent Office
Prior art keywords
gas
sensor according
electrode
gas sensor
electrodes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06806778A
Other languages
German (de)
French (fr)
Inventor
Berndt Cramer
Sabine Thiemann-Handler
Mario Roessler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
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Filing date
Publication date
Application filed by Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of EP1934590A1 publication Critical patent/EP1934590A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—Specially adapted to detect a particular component
    • G01N33/0047—Specially adapted to detect a particular component for organic compounds
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/406—Cells and probes with solid electrolytes
    • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
    • G01N27/4073—Composition or fabrication of the solid electrolyte
    • G01N27/4074—Composition or fabrication of the solid electrolyte for detection of gases other than oxygen
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0006—Calibrating gas analysers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—Specially adapted to detect a particular component
    • G01N33/0037—Specially adapted to detect a particular component for NOx
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—Specially adapted to detect a particular component
    • G01N33/0054—Specially adapted to detect a particular component for ammonia
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

  • the present invention relates to a gas sensor according to the preamble of claim 1.
  • sensors For the detection of gas components or for the determination of a gas concentration in measuring gas mixtures is known to use sensors that are constructed on the basis of a solid electrolyte and operated according to the mixed potential principle.
  • the mixing potential is formed between two electrodes connected by means of the solid electrolyte and represents a measure of the gas components to be detected occurring in the gas mixture.
  • This mixed potential between the two preferably platinum-containing or oxide electrodes which may optionally be combined with other chemical elements, depending on the field of use, sometimes has high cross sensitivities to other, not to be detected desired gas components, in particular to oxygen and / or hydrocarbons.
  • This cross-sensitivity falsifies the measurement signal, so that, in particular at low concentrations of gas components to be detected, eg ⁇ 50 ppm, strong measurement inaccuracies due to deviation of the measured value from the actual concentration can be determined.
  • the object of the present invention is therefore to improve a measuring sensor according to the type set forth.
  • the invention relates to a gas sensor for detecting a gas concentration in a measurement gas mixture, in particular a nitrogen compound or in general an oxidizable substance, with a solid electrolyte, which ion-conductively connects a first and a second electrode, wherein the first electrode has a high activity with respect to oxidation or reduction of Having shown gas component, and the second electrode has a low related activity.
  • the sensor is characterized in that the influence on the activity with respect to oxidation or reduction of the gas component to be determined by free oxygen present in the sample gas mixture is approximately equally pronounced on both electrodes.
  • the two electrodes also have a relatively low differential activity with respect to hydrocarbon compounds compared to their activity with respect to the gas to be sensed.
  • a sensor constructed in this way can thus provide a measurement signal which, compared to the first embodiment, has an even lower cross-sensitivity with respect to gas components not intended for the determination.
  • the structure of such a sensor provides that the two electrodes have the same gas-sensitive base material.
  • the gas-sensitive base material for this purpose can be composed of two chemical elements, or a cermet with two further elements, wherein a first connection structure between the two chemical elements at the first electrode is different from a second connection. formation structure between the two chemical elements may be formed on the second electrode.
  • Two preferred chemical elements for forming the two electrodes with such material bonding methods are gold (Au) and platinum (Pt).
  • Au gold
  • Pt platinum
  • a built-up with such an electrode sensor is particularly well suited to, for example, NH 3, NO x, the hydrocarbon compounds as a gas component of a measurement to determine the gas mixture.
  • a gas sensor constructed in this way is that, for the determination of the concentration of the desired gas component, even both electrodes can be exposed to the sample gas mixture to be investigated.
  • no further electrode is required, as well as no reference gas electrode exposed to a reference gas.
  • the sensor can thus be manufactured with a minimum number of process steps. It only requires the formation of a carrier Mentes and the arrangement of the two electrodes according to the invention, and optionally a heating element and the relevant electrical connection lines to provide a functional sensor available.
  • a sensor may further be provided, at least in part, with a protective layer or the like in order, for example, to achieve an increase in the operating time, or possibly to adapt the sensor to special application requirements.
  • Figures 1 and 2 are schematic sectional views of two differently constructed, inventive sensors and
  • FIG. 3 shows a diagram with measurement signals of the sensor according to the invention.
  • FIGS 1 and 2 show schematic sectional views of a sensor 1 according to the invention in two different embodiments.
  • the sensor 1 comprises a carrier 2, which preferably consists of yttrium-stabilized zirconium dioxide (YSZ) and at the same time acts as an ion-conducting electrolyte between the two electrodes 3 and 4 arranged on it.
  • YSZ yttrium-stabilized zirconium dioxide
  • the first electrode 3 has a high activity with respect to oxidation or reduction of the gas component to be sensed.
  • the second electrode has a low activity in comparison thereto.
  • both electrodes are designed such that the influence on the activity with regard to oxidation or reduction of the gas component to be determined by free oxygen present in the sample gas mixture is approximately equally pronounced on both electrodes.
  • the measurement signal very little to no disturbing oxygen cross sensitivity
  • a sensor constructed also has a relatively low cross-sensitivity to hydrocarbon compounds in comparison to its sensitivity to the gas component to be measured.
  • the two electrodes 3, 4 may be formed of the same gas-sensitive base material, this in turn composed of two chemical elements, or may be a cermet with two additional elements.
  • connection structure between the two chemical elements of the electrode 3 is formed differently from a connection structure between the two chemical elements of the electrode 4. It has proven to be particularly favorable to produce a connection structure between the two chemical elements by means of a galvanic material connection method and the second by means of a sintering process.
  • Au gold
  • Pt platinum
  • the electrode whose connection structure is produced by means of a sintering process, which is also called “co-firing” has virtually no influence on the oxidation or reduction of the gas component to be sensed. It acts so strongly catalytically that all the components of the gas component to be measured, in particular NH 3 , are reacted at the surface which is effective for signal detection and no appreciable concentration is formed.
  • the gas component to be sensed has virtually no influence on the oxygen activity and thus on the formation of potential.
  • the second electrode with the galvanically produced connection structure between the two chemical elements which is formed in a particularly preferred embodiment as a gold-plated platinum electrode, due to their lower catalytic activity, a very sensitive in this respect.
  • the NH 3 is not fully reacted and reduces the activity of the oxygen at the surface.
  • both electrodes can be exposed directly to the sample gas mixture for determining the concentration of the desired gas component.
  • the two electrodes 3, 4 are arranged on two opposite sides, top and bottom, of the solid electrolyte 2 serving as support.
  • FIG. 2 shows a modified embodiment in that both electrodes 3, 4 are formed on the same side of the carrier 2.
  • the contacting of the two electrodes is symbolically represented by the terminals 6, 7.
  • the two sensors according to Figures 1 and 2 are further provided with a heating element 5.
  • One possible method of manufacturing such a sensor is a screen printing method using e.g. serve two so-called ceramic sheets as the top and bottom of the sensor, between which a heating element can be arranged. They are in turn each provided with one of the two measuring electrodes, corresponding to the embodiment of Figure 1.
  • a Pt-Au paste is used, for the other a Pt paste.
  • FIG. 3 shows a diagram 8 with a measuring signal 9 in reference to a concentration signal 10 of a gas component in a measuring gas mixture.
  • the time t in s is plotted from 0 to 1200.
  • the height of the measurement signal in mV is scaled from 0 to 50.
  • the right-hand vertical scaling represents, with the values from 0 to 6, the concentration of the measured gas components to be multiplied by the factor 150 ppm, in this case NH 3 , linear.

Abstract

The present invention relates to a gas sensor for sensing a gas concentration in a test gas mixture, in particular a nitrogen compound, having a solid electrolyte which connects a first electrode and a second electrode in an ion-conducting manner, the first electrode having a high activity with respect to oxidation or reduction of the gas component to be sensed, and the second electrode having a low activity in this respect. It is distinguished in that the effect on the activity with respect to oxidation or reduction of the gas component to be determined due to free oxygen present in the test gas mixture is about equally strongly expressed at both electrodes.

Description

"Gassensor""Gas sensor"
Die vorliegende Erfindung betrifft einen Gassensor nach dem Oberbegriff des Anspruchs 1.The present invention relates to a gas sensor according to the preamble of claim 1.
Stand der TechnikState of the art
Zum Nachweis von Gaskomponenten oder zur Bestimmung einer Gaskonzentration in Messgasgemischen ist bekannt, Sensoren zu verwenden, die auf der Basis eines Festkörperelektrolyten aufgebaut sind und nach dem Mischpotenzial-Prinzip betrieben werden. Das Mischpotenzial bildet sich zwischen zwei mittels des Festkörperelektrolyten verbundenen Elektroden aus und stellt ein Maß für die im Gasgemisch vorkommenden, nachzuweisenden Gaskomponenten dar.For the detection of gas components or for the determination of a gas concentration in measuring gas mixtures is known to use sensors that are constructed on the basis of a solid electrolyte and operated according to the mixed potential principle. The mixing potential is formed between two electrodes connected by means of the solid electrolyte and represents a measure of the gas components to be detected occurring in the gas mixture.
Dieses Mischpotenzial zwischen den beiden vorzugsweise platinhaltigen oder oxidischen Elektroden, welche gegebenenfalls mit weiteren chemischen Elementen kombiniert sein können, weist je nach Einsatzbereich zum Teil hohe Querempfindlichkeiten gegenüber weiteren, nicht zu detektieren gewünschten Gaskomponenten auf, insbesondere gegenüber Sauerstoff und/oder Kohlenwasserstoffen. Diese Querempfindlichkeit verfälscht das Messsignal, so dass insbesondere bei geringen Konzentrationen nachzuweisender Gaskomponenten, z.B. <50 ppm, starke Messungenauigkeiten durch Abweichung des Messwertes von dem der tatsächlichen Konzentration entsprechenden festzustellen sind. This mixed potential between the two preferably platinum-containing or oxide electrodes, which may optionally be combined with other chemical elements, depending on the field of use, sometimes has high cross sensitivities to other, not to be detected desired gas components, in particular to oxygen and / or hydrocarbons. This cross-sensitivity falsifies the measurement signal, so that, in particular at low concentrations of gas components to be detected, eg <50 ppm, strong measurement inaccuracies due to deviation of the measured value from the actual concentration can be determined.
Aufgabe und Vorteile der ErfindungPurpose and advantages of the invention
Aufgabe der vorliegenden Erfindung ist daher, einen Messsensor nach der eingangs dargelegten Art zu verbessern.The object of the present invention is therefore to improve a measuring sensor according to the type set forth.
Diese Aufgabe wird durch die Merkmale des Anspruchs 1 gelöst. In den Unteransprüchen sind vorteilhafte und zweckmäßige Weiterbildungen der Erfindung angegeben.This object is solved by the features of claim 1. In the dependent claims advantageous and expedient developments of the invention are given.
Dementsprechend betrifft die Erfindung einen Gassensor zum Nachweis einer Gaskonzentration in einem Messgasgemisch, insbesondere einer Stickstoffverbindung oder allgemein einer oxydierbaren Substanz, mit einem Festkörperelektrolyten, der eine erste und eine zweite Elektrode ionenleitend verbindet, wobei die erste Elektrode eine hohe Aktivität bezüglich Oxidation bzw. Reduktion der nachzuweisenden Gaskomponente aufweist, und die zweite Elektrode eine geringe diesbezügliche Aktivität. Der Sensor zeichnet sich erfindungsgemäß dadurch aus, dass der Einfluss auf die Aktivität bezüglich Oxidation bzw. Reduktion der zu bestimmenden Gaskomponente durch im Messgasgemisch vorhandenen freien Sauerstoff an beiden Elektroden in etwa gleich stark ausgeprägt ist. Dadurch, dass die beiden Elektroden derart ausgebildet sind, dass die Bindung bzw. Freigabe von Sauerstoffionen an der Dreiphasengrenze der beiden Elektroden mit dem Festelektrolyten und der Gasphase in etwa gleich stark bzw. gleich gering von dem im Messgas vorhandenen, freien Sauerstoff beeinflusst ist, ist der diesbezügliche Mischpotenzialanteil des Sensors für die Auswertung der Gaskonzentration der zu bestimmenden Gaskomponente weitest- gehend vernachlässigbar.Accordingly, the invention relates to a gas sensor for detecting a gas concentration in a measurement gas mixture, in particular a nitrogen compound or in general an oxidizable substance, with a solid electrolyte, which ion-conductively connects a first and a second electrode, wherein the first electrode has a high activity with respect to oxidation or reduction of Having shown gas component, and the second electrode has a low related activity. According to the invention, the sensor is characterized in that the influence on the activity with respect to oxidation or reduction of the gas component to be determined by free oxygen present in the sample gas mixture is approximately equally pronounced on both electrodes. Characterized in that the two electrodes are formed such that the binding or release of oxygen ions at the three-phase boundary of the two electrodes with the solid electrolyte and the gas phase is influenced approximately equal to or equal to the free oxygen present in the measurement gas, is the related mixed potential component of the sensor for the evaluation of the gas concentration of the gas component to be determined largely negligible.
Insbesondere bevorzugt ist, wenn die beiden Elektroden auch bezüglich Kohlenwasserstoffverbindungen eine, im Vergleich zu ihrer Aktivität bezüglich des zu sensierenden Gases verhältnismäßig geringe unterschiedliche Aktivität aufweisen. Ein derart aufgebauter Sensor kann somit ein Messsignal zur Verfügung stellen, welches gegenüber der ersten Ausführungsform eine noch geringere Querempfindlichkeit bezüglich nicht zur Bestimmung vorgesehener Gaskomponenten aufweist.It is particularly preferred if the two electrodes also have a relatively low differential activity with respect to hydrocarbon compounds compared to their activity with respect to the gas to be sensed. A sensor constructed in this way can thus provide a measurement signal which, compared to the first embodiment, has an even lower cross-sensitivity with respect to gas components not intended for the determination.
Der Aufbau eines derartigen Sensors sieht vor, dass die beiden Elektroden das gleiche gassensitive Grundmaterial aufweisen. Insbesondere vorteilhaft kann das gassensitive Grundmaterial hierzu aus zwei chemischen Elementen zusammengesetzt sein, oder einem Cermet mit zwei weiteren Elementen, wobei eine erste Verbindungsstruktur zwischen den beiden chemischen Elementen an der ersten Elektrode unterschiedlich von einer zweiten Verbin- dungsstruktur zwischen den beiden chemischen Elementen an der zweiten Elektrode ausgebildet sein kann. Damit ist es beispielsweise möglich, die beiden Elektroden mit unterschiedlich starker katalytischer Wirkung bezüglich einer zu bestimmenden Gaskomponente eines Messgasgemisches auszubilden, so dass die eine Elektrode eine sehr starke und die andere Elektrode eine geringe, vorzugsweise sogar gar keine Aktivität bezüglich der zu sensierenden Gaskomponente aufweist.The structure of such a sensor provides that the two electrodes have the same gas-sensitive base material. Particularly advantageously, the gas-sensitive base material for this purpose can be composed of two chemical elements, or a cermet with two further elements, wherein a first connection structure between the two chemical elements at the first electrode is different from a second connection. formation structure between the two chemical elements may be formed on the second electrode. Thus, it is for example possible to form the two electrodes with different strong catalytic effect with respect to a gas component to be determined a sample gas mixture, so that the one electrode has a very strong and the other electrode a low, preferably even no activity with respect to the gas component to be sensed.
Für die Reduzierung der Sauerstoffquerempfindlichkeit ist bei Verwendung gleicher chemischer Grundelemente für die Herstellung der Elektroden deren Präparation von wesentlicher Bedeutung. Diese beeinflusst die späteren chemischen Eigenschaften der betreffenden Elektrode ganz wesentlich.When using the same basic chemical elements for the preparation of the electrodes whose preparation is essential for the reduction of oxygen interference. This substantially influences the later chemical properties of the electrode in question.
Insbesondere gut geeignet für die Ausbildung zweier Elektroden mit stark unterschiedlicher Aktivitätseigenschaften bezüglich einer nachzuweisenden Gaskomponente, aber mit geringer Sauerstoffquerempfindlichkeit, sind zwei verschiedene Verbindungsstrukturen zwischen den beiden chemischen Elementen, wie sie z.B. durch galvanische Materialverbindungsverfahren bzw. durch Sinterprozesse entstanden sind.Particularly well suited for the formation of two electrodes with greatly different activity characteristics with respect to a gas component to be detected, but with low oxygen cross sensitivity, are two different bonding structures between the two chemical elements, as e.g. originated by galvanic material bonding processes or by sintering processes.
Diese massive Reduzierung der Sauerstoffquerempfϊndlichkeit und auch eine deutliche Reduzierung der Querempfmdlichkeiten bezüglich Kohlenwasserstoffen konnte durch Versuche nachgewiesen werden, bei denen die erste Elektrode den einen und die zweite Elektrode den anderen Strukturaufbau zur Verbindung zweier gleicher chemischer Elemente aufwies.This massive reduction in oxygen cross-sensitivity and also a significant reduction in cross-sensitivity to hydrocarbons could be demonstrated by experiments in which the first electrode had one and the second electrode the other structure for connecting two identical chemical elements.
Zwei bevorzugte chemische Elemente zur Ausbildung der beiden Elektroden mit derartigen Materialverbindungsverfahren sind Gold (Au) und Platin (Pt). Ein mit solchen Elektroden aufgebauter Sensor ist insbesondere gut dazu geeignet, z.B. NH3, NOx der Kohlenwasserstoffverbindungen als Gaskomponente eines Messgasgemisches zu bestimmen.Two preferred chemical elements for forming the two electrodes with such material bonding methods are gold (Au) and platinum (Pt). A built-up with such an electrode sensor is particularly well suited to, for example, NH 3, NO x, the hydrocarbon compounds as a gas component of a measurement to determine the gas mixture.
Ein weiterer großer Vorteil eines derart aufgebauten Gassensors liegt darin, dass zur Konzentrationsbestimmung der gesuchten Gaskomponente sogar beide Elektroden dem zu untersuchenden Messgasgemisch ausgesetzt werden können. Zur Erzeugung des den Konzentrationswert der zu bestimmenden Gaskomponente im Messgasgemisch wiedergebenden Signals ist keine weitere Elektrode erforderlich, ebenso keine einem Referenzgas ausgesetzte Referenzgaselektrode. Der Sensor kann somit mit einer minimalen Anzahl an Verfahrensschritten hergestellt werden. Es bedarf lediglich der Ausbildung eines Trägerele- mentes und der Anordnung der beiden erfindungsgemäßen Elektroden, sowie gegebenenfalls einem Heizelement und der betreffenden elektrischen Verbindungsleitungen, um einen funktionstüchtigen Sensor zur Verfügung zu stellen. Selbstverständlich kann ein solcher Sensor im Weiteren, wenigstens teilweise mit einer Schutzschicht oder dergleichen versehen sein, um z.B. eine Erhöhung der Betriebsdauer zu erzielen, oder eventuell den Sensor an spezielle Einsatzerfordernisse anzupassen.Another great advantage of a gas sensor constructed in this way is that, for the determination of the concentration of the desired gas component, even both electrodes can be exposed to the sample gas mixture to be investigated. In order to generate the signal representing the concentration value of the gas component to be determined in the sample gas mixture, no further electrode is required, as well as no reference gas electrode exposed to a reference gas. The sensor can thus be manufactured with a minimum number of process steps. It only requires the formation of a carrier Mentes and the arrangement of the two electrodes according to the invention, and optionally a heating element and the relevant electrical connection lines to provide a functional sensor available. Of course, such a sensor may further be provided, at least in part, with a protective layer or the like in order, for example, to achieve an increase in the operating time, or possibly to adapt the sensor to special application requirements.
Ausführungsbeispielembodiment
Die Erfindung wird anhand der Zeichnungen und der nachfolgenden, darauf Bezug nehmenden Beschreibung näher erläutert. Es zeigen:The invention will be explained in more detail with reference to the drawings and the following description taken in conjunction therewith. Show it:
Figur 1 und 2 schematische Schnittdarstellungen zweier unterschiedlich aufgebauter, erfindungsgemäßer Sensoren undFigures 1 and 2 are schematic sectional views of two differently constructed, inventive sensors and
Figur 3 ein Diagramm mit Messsignalen des erfindungsgemäßen Sensors.FIG. 3 shows a diagram with measurement signals of the sensor according to the invention.
Im Detail zeigen die Figuren 1 und 2 schematische Schnittdarstellungen eines erfindungsgemäßen Sensors 1 in zwei unterschiedlichen Ausführungsformen. Der Sensor 1 umfasst einen Träger 2, welcher vorzugsweise aus yttriumstabilisiertem Zirkondioxid (YSZ) besteht und gleichzeitig als ionenleitender Elektrolyt zwischen den beiden an ihm angeordneten Elektroden 3 und 4 fungiert.In detail, Figures 1 and 2 show schematic sectional views of a sensor 1 according to the invention in two different embodiments. The sensor 1 comprises a carrier 2, which preferably consists of yttrium-stabilized zirconium dioxide (YSZ) and at the same time acts as an ion-conducting electrolyte between the two electrodes 3 and 4 arranged on it.
Die erste Elektrode 3 weist dabei eine hohe Aktivität bezüglich Oxidation bzw. Reduktion der zu sensierenden Gaskomponente auf. Die zweite Elektrode weist eine demgegenüber geringe diesbezügliche Aktivität auf. Erfindungsgemäß sind beide Elektroden so ausgebildet, dass der Einfluss auf die Aktivität bezüglich Oxidation bzw. Reduktion der zu bestimmenden Gaskomponente durch im Messgasgemisch vorhandenen freien Sauerstoff an beiden Elektroden in etwa gleich stark ausgeprägt ist.The first electrode 3 has a high activity with respect to oxidation or reduction of the gas component to be sensed. The second electrode has a low activity in comparison thereto. According to the invention, both electrodes are designed such that the influence on the activity with regard to oxidation or reduction of the gas component to be determined by free oxygen present in the sample gas mixture is approximately equally pronounced on both electrodes.
Neben dieser, das Messsignal sehr gering bis gar nicht störenden Sauerstoff- Querempfindlichkeit weist ein derart aufgebauter Sensor auch noch eine verhältnismäßig geringe Querempfindlichkeit bezüglich Kohlenwasserstoff- Verbindungen im Vergleich zu seiner Empfindlichkeit bezüglich der zu messenden Gaskomponente auf. Die beiden Elektroden 3, 4 können dazu aus dem gleichen gassensitiven Grundmaterial ausgebildet sein, wobei dieses wiederum aus zwei chemischen Elementen zusammengesetzt, oder ein Cermet mit zwei zusätzlichen Elementen sein kann.In addition to this, the measurement signal very little to no disturbing oxygen cross sensitivity, such a sensor constructed also has a relatively low cross-sensitivity to hydrocarbon compounds in comparison to its sensitivity to the gas component to be measured. For this purpose, the two electrodes 3, 4 may be formed of the same gas-sensitive base material, this in turn composed of two chemical elements, or may be a cermet with two additional elements.
In einer bevorzugten Ausführungsform ist dabei die Verbindungsstruktur zwischen den beiden chemischen Elementen der Elektrode 3 unterschiedlich von einer Verbindungsstruktur zwischen den beiden chemischen Elementen der Elektrode 4 ausgebildet. Als besonders günstig hat es sich herausgestellt, die eine Verbindungsstruktur zwischen den beiden chemischen Elementen mittels eines galvanischen Materialverbindungsverfahrens herzustellen und die zweite mittels eines Sinterprozesses.In a preferred embodiment, the connection structure between the two chemical elements of the electrode 3 is formed differently from a connection structure between the two chemical elements of the electrode 4. It has proven to be particularly favorable to produce a connection structure between the two chemical elements by means of a galvanic material connection method and the second by means of a sintering process.
Insbesondere vorteilhaft eignen sich dazu die beiden chemischen Elemente Gold (Au) und Platin (Pt). Bei Versuchen wurde festgestellt, dass die Elektrode, deren Verbindungsstruktur mittels Sinterprozess, welcher auch "Co-Firing" genannt wird, hergestellt ist, so gut wie keinen Einfiuss auf die Oxidation bzw. Reduktion der zu sensierenden Gaskomponente aufweist. Sie wirkt derart stark katalytisch, dass alle Anteile der zu messenden Gaskomponente, insbesondere NH3, an der für die Signalerfassung wirksamen Oberfläche umgesetzt werden und sich keine nennenswerte Konzentration ausbildet. An einer solchen Elektrode hat die zu sensierende Gaskomponente praktisch keinen Einfiuss auf die Sauerstoffaktivität und damit auf die Potenzialbildung.Particularly advantageous for this purpose are the two chemical elements gold (Au) and platinum (Pt). In experiments, it was found that the electrode whose connection structure is produced by means of a sintering process, which is also called "co-firing", has virtually no influence on the oxidation or reduction of the gas component to be sensed. It acts so strongly catalytically that all the components of the gas component to be measured, in particular NH 3 , are reacted at the surface which is effective for signal detection and no appreciable concentration is formed. At such an electrode, the gas component to be sensed has virtually no influence on the oxygen activity and thus on the formation of potential.
Demgegenüber hat die zweite Elektrode mit der galvanisch hergestellten Verbindungsstruktur zwischen den beiden chemischen Elementen, welche in einer besonders bevorzugten Ausführungsform als vergoldete Platinelektrode ausgebildet ist, aufgrund ihrer geringeren katalytischen Aktivität, ein diesbezüglich sehr empfindliches Ansprechverhalten. Das NH3 wird nicht vollständig umgesetzt und reduziert die Aktivität des Sauerstoffs an der Oberfläche.In contrast, the second electrode with the galvanically produced connection structure between the two chemical elements, which is formed in a particularly preferred embodiment as a gold-plated platinum electrode, due to their lower catalytic activity, a very sensitive in this respect. The NH 3 is not fully reacted and reduces the activity of the oxygen at the surface.
Insbesondere vorteilhaft ist weiterhin, dass beide Elektroden direkt dem Messgasgemisch zur Bestimmung der Konzentration der gesuchten Gaskomponente aussetzbar sind. In der Ausfuhrungsförm nach Figur 1 sind die beiden Elektroden 3, 4 an zwei sich gegenüberliegenden Seiten, oben und unten, des als Träger dienenden Festkörperelektrolyten 2 angeordnet. Die Figur 2 zeigt eine demgegenüber dahingehend abgewandelte Ausführungsform, dass beide Elektroden 3, 4 an der gleichen Seite des Trägers 2 ausgebildet sind. Die Kontaktierung der beiden Elektroden ist jeweils symbolisch durch die Anschlüsse 6, 7 dargestellt. Um den Sensor auf eine bestimmte Temperatur einstellen zu können, welche von der zu bestimmenden Gaskomponente abhängig sein kann, sind die beiden Sensoren nach den Figuren 1 und 2 im Weiteren noch mit einem Heizelement 5 versehen.It is furthermore particularly advantageous that both electrodes can be exposed directly to the sample gas mixture for determining the concentration of the desired gas component. In the embodiment according to FIG. 1, the two electrodes 3, 4 are arranged on two opposite sides, top and bottom, of the solid electrolyte 2 serving as support. FIG. 2 shows a modified embodiment in that both electrodes 3, 4 are formed on the same side of the carrier 2. The contacting of the two electrodes is symbolically represented by the terminals 6, 7. To be able to set the sensor to a certain temperature, which depends on may be dependent on the gas component to be determined, the two sensors according to Figures 1 and 2 are further provided with a heating element 5.
Ein mögliches Herstellungsverfahren eines solchen Sensors ist ein Siebdruckverfahren, bei dem z.B. zwei so genannte Keramikfolien als Ober- und Unterseite des Sensors dienen, zwischen denen ein Heizelement angeordnet sein kann. Sie sind ihrerseits jeweils mit einer der beiden Messelektroden versehen, entsprechend der Ausführungsform nach Figur 1. Für die Ausbildung der einen Elektrode wird eine Pt-Au-Paste verwendet, für die andere eine Pt-Paste. Nach einem zur Härtung und Verdichtung des Sensorelements vorgesehenen Sintervorgang kann die zweite Elektrode, die Pt-Elektrode, z. B. mittels eines elektrochemischen Abscheideverfahrens aus einer HAuCU-Lösung vergoldet werden. Damit sind zwei Elektroden mit unterschiedlichen Verbindungsstrukturen zwischen den beiden chemischen Elementen Platin und Gold an dem Sensor ausgebildet, die den in Versuchen nachgewiesenen erfindungsgemäßen Vorteil bewirken.One possible method of manufacturing such a sensor is a screen printing method using e.g. serve two so-called ceramic sheets as the top and bottom of the sensor, between which a heating element can be arranged. They are in turn each provided with one of the two measuring electrodes, corresponding to the embodiment of Figure 1. For the formation of one electrode, a Pt-Au paste is used, for the other a Pt paste. After a sintering process provided for hardening and densifying the sensor element, the second electrode, the Pt electrode, z. B. gilded by means of an electrochemical deposition of a HAuCU solution. Thus, two electrodes with different connection structures between the two chemical elements platinum and gold are formed on the sensor, which effect the inventive advantage proven in tests.
Die Figur 3 zeigt ein Diagramm 8, mit einem Messsignal 9 in Referenz zu einem Konzentrationssignal 10 einer Gaskomponente in einem Messgasgemisch. An der horizontalen Achse ist die Zeit t in s von 0 bis 1200 aufgetragen. An der linken vertikalen Achse ist die Höhe des Messsignals in mV von 0 bis 50 skaliert. Die rechte vertikale Skalierung stellt mit den Werten von 0 bis 6 die mit dem Faktor 150 ppm zu multiplizierende Konzentration der gemessenen Gaskomponenten, hier im vorliegenden Fall NH3, linear dar.FIG. 3 shows a diagram 8 with a measuring signal 9 in reference to a concentration signal 10 of a gas component in a measuring gas mixture. On the horizontal axis the time t in s is plotted from 0 to 1200. On the left vertical axis, the height of the measurement signal in mV is scaled from 0 to 50. The right-hand vertical scaling represents, with the values from 0 to 6, the concentration of the measured gas components to be multiplied by the factor 150 ppm, in this case NH 3 , linear.
Die vier in Folge durchgeführten Messungen wurden mit unterschiedlichen Sauerstoffkonzentrationen von 8%, 6%, 4% und 2% (von links nach rechts in der Darstellung wiedergegeben) durchgeführt. Hierbei wird insbesondere auf die hohe Sensitivität des erfindungsgemäßen Sensors bei kleinen NH3-Flüssen und die dabei nachweisliche, geringe Sauer- stoff-Querempfindlichkeit hingewiesen. Erst bei sehr geringen Sauerstoffkonzentrationen kann eine geringe Abnahme der Signalhöhe des mit 5 kΩ belasteten erfindungsgemäßen Sensors beobachtet werden. Neben der guten NH3-Empfmdlichkeit ist dieser erfmdungs- gemäße Sensor auch für die Bestimmung von NOx-Gaskomponenten, insbesondere NO2 und für Kohlenwasserstoff hervorragend einsetzbar. The four consecutive measurements were performed with different oxygen concentrations of 8%, 6%, 4% and 2% (shown from left to right in the illustration). In this connection, particular attention is drawn to the high sensitivity of the sensor according to the invention in the case of small NH 3 flows and the small oxygen cross-sensitivity which can be demonstrated. Only at very low oxygen concentrations can a small decrease in the signal level of the sensor loaded with 5 kΩ be observed. In addition to the good NH 3 -Empfmdlichkeit this erfmdungsgemäße sensor is also excellent for the determination of NO x gas components, in particular NO 2 and for hydrocarbon.

Claims

Ansprüche: Claims:
1. Gassensor zur Sensierung einer Gaskonzentration in einem Messgasgemisch, insbesondere einer Stickstoffverbindung oder einer Kohlenwasserstoffverbindung, mit einem Festkörperelektrolyten, der eine erste und eine zweite Elektrode ionenleitend verbindet, wobei die erste Elektrode eine hohe Aktivität bezüglich Oxidation bzw. Reduktion der zu sensierenden Gaskomponente aufweist, und die zweite Elektrode eine geringe diesbezügliche Aktivität, dadurch gekennzeichnet, dass der Einfluss auf die Aktivität bezüglich Oxidation bzw. Reduktion der zu bestimmenden Gaskomponente durch im Messgasgemisch vorhandenen freien Sauerstoff an beiden Elektroden in etwa gleich stark ausgeprägt ist.A gas sensor for sensing a gas concentration in a measurement gas mixture, in particular a nitrogen compound or a hydrocarbon compound, comprising a solid electrolyte which connects a first and a second electrode in an ion-conducting manner, wherein the first electrode has a high activity with regard to oxidation or reduction of the gas component to be sensed, and the second electrode has a low activity in this respect, characterized in that the influence on the activity with respect to oxidation or reduction of the gas component to be determined by free oxygen present in the sample gas mixture at both electrodes is approximately equally pronounced.
2. Gassensor nach Anspruch 1, dadurch gekennzeichnet, dass der Einfluss auf die Aktivität bezüglich Oxidation bzw. Reduktion der zu bestimmenden Gaskomponente durch im Messgasgemisch vorhandenen Kohlenwasserstoff- Verbindungen an beiden Elektroden in etwa gleich stark ausgeprägt ist.2. Gas sensor according to claim 1, characterized in that the influence on the activity with respect to oxidation or reduction of the gas component to be determined by present in the sample gas mixture hydrocarbon compounds at both electrodes is approximately equally pronounced.
3. Gassensor nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die beiden Elektroden das gleiche gassensitive Grundmaterial aufweisen.3. Gas sensor according to claim 1 or 2, characterized in that the two electrodes have the same gas-sensitive base material.
4. Gassensor nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, dass das gassensitive Grundmaterial aus zwei chemischen Elementen zusammengesetzt ist.4. Gas sensor according to claim 1, 2 or 3, characterized in that the gas-sensitive base material is composed of two chemical elements.
5. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass das gassensitive Grundmaterial aus ternären oder quarternären Verbindungen zusammengesetzt ist.5. Gas sensor according to one of the preceding claims, characterized in that the gas-sensitive base material is composed of ternary or quaternary compounds.
6. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine erste Verbindungsstruktur zwischen den beiden chemischen Elementen an der ersten Elektrode unterschiedlich von einer zweiten Verbindungsstruktur zwischen den beiden chemischen Elementen an der zweiten Elektrode ausgebildet ist. 6. Gas sensor according to one of the preceding claims, characterized in that a first connection structure between the two chemical elements at the first electrode is formed differently from a second connection structure between the two chemical elements at the second electrode.
7. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine ternäre oder quarternäre Verbindung unterschiedlich von einer zweiten Verbindungsstruktur zwischen den beiden chemischen Elementen an der zweiten Elektrode ausgebildet ist.7. Gas sensor according to one of the preceding claims, characterized in that a ternary or quaternary compound is formed differently from a second connection structure between the two chemical elements at the second electrode.
8. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die erste Verbindungsstruktur als eine bei einem galvanischen Materialverbindungsverfahren entstandene Struktur ausgebildet ist.8. Gas sensor according to one of the preceding claims, characterized in that the first connection structure is formed as a resulting in a galvanic material bonding method structure.
9. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die zweite Verbindungsstruktur als bei einem Sinterprozess entstandene Struktur ausgebildet ist.9. Gas sensor according to one of the preceding claims, characterized in that the second connection structure is formed as formed during a sintering process structure.
10. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass ein chemisches Element Gold (Au) ist.10. Gas sensor according to one of the preceding claims, characterized in that a chemical element is gold (Au).
11. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass ein chemisches Element Platin (Pt) ist.11. Gas sensor according to one of the preceding claims, characterized in that a chemical element is platinum (Pt).
12. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die beiden Elektroden ein Messsignal frei von einem Referenzgasbezug liefern.12. Gas sensor according to one of the preceding claims, characterized in that the two electrodes deliver a measuring signal free of a reference gas reference.
13. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass ein chemisches Element Pd, Cu, W, V, Ag oder Ir ist. 13. Gas sensor according to one of the preceding claims, characterized in that a chemical element Pd, Cu, W, V, Ag or Ir.
EP06806778A 2005-09-30 2006-09-19 Gas sensor Withdrawn EP1934590A1 (en)

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