WO2007096203A1 - Gas sensor - Google Patents

Gas sensor Download PDF

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Publication number
WO2007096203A1
WO2007096203A1 PCT/EP2007/050129 EP2007050129W WO2007096203A1 WO 2007096203 A1 WO2007096203 A1 WO 2007096203A1 EP 2007050129 W EP2007050129 W EP 2007050129W WO 2007096203 A1 WO2007096203 A1 WO 2007096203A1
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Prior art keywords
hydrogen
gas
gas sensor
sensor according
electrode
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PCT/EP2007/050129
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German (de)
French (fr)
Inventor
Ralf Liedtke
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Robert Bosch Gmbh
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Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Priority to EP07703682A priority Critical patent/EP1989539A1/en
Publication of WO2007096203A1 publication Critical patent/WO2007096203A1/en

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    • 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
    • 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
    • G01N27/416—Systems
    • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
    • G01N27/419—Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells
    • 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—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0054—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 for determining a hydrogen-containing gas component and / or its concentration in a measuring gas, according to the preamble of claim 1.
  • EP 0 693 180 B1 discloses an ammonia sensor which operates on an amperometric basis, wherein a membrane permeable to ammonia seals off the sensor to form a sample gas sample.
  • the electrolyte contains a metal ion which is not oxidizable by atmospheric oxygen in aqueous solution and which forms a complex, oxygen-oxidizable metal ion with ammonia.
  • This sensor is designed for room temperature and / or aqueous solutions. Its field of application is accordingly limited.
  • WO 01/48466 A2 discloses a sensor element of a gas sensor for determining the concentration of hydrogen present in a gas mixture or of hydrogen-containing gas components such as ammonia or hydrocarbons.
  • an emf caused by different hydrogen or proton concentration at two measuring or reference electrodes is determined by measuring the applied electrical voltage in the so-called "Nernst cell” operating mode.
  • the present invention is based on the object to improve a gas sensor for the determination of hydrogen-containing gas components in a sample gas, in particular NH3 shares, according to the manner outlined in the introduction.
  • the invention relates to a gas sensor for determining a hydrogen-containing gas component and / or its concentration in a measurement gas, in particular for the determination of NH 3 , comprising two protons conductively connected by a proton conductor electrodes, wherein between a measurement gas ausiqueden sensor area and a first, with respect to a Splitting the hydrogen-containing gas component catalytically active electrode is disposed a diffusion barrier.
  • the gas sensor is characterized in that the proton conductor is connected to the two electrodes as a hydrogen ion pumping cell.
  • a pump cell is understood as meaning an amperometrically operated electrolyte contacted via two electrodes. That is, at the two electrodes is a potential difference, and caused by the ion migration through the electrolyte electric current is z. B. detected as a measure of the concentration of hydrogen in the sample gas. The same applies of course to a proton conductor.
  • the hydrogen proton conductor formed as a solid may be composed of barium zirconate, in particular of doped barium zirconate.
  • the construction of such a gas sensor can be carried out, for example, in the form of a planar sensor element.
  • a basic ceramic for example, an yttrium-stabilized zirconia
  • the diffusion barrier serves as a gas resistance between the sample gas to be tested for specific proportions and / or concentrations and a sample gas sample chamber. It delimits the sample gas sample chamber from the sensor area to be exposed to the sample gas. In this sensor area, it may be z. B. may be an opening on one side of the sensor.
  • the so-called “hydrogen pump” formed from the two electrodes and the hydrogen proton conductor pumps out the hydrogen (H) formed in the splitting of ammonia (NH 3 ) in ionized form (H + ) from the sample gas sample chamber For example, back to the room in which the sample gas to be tested is located, but it would also be conceivable to pump it off in an area which is separate from this room.
  • this first electrode may be made of a suitably suitable material, for example of platinum, in particular of pure platinum.
  • H total hydrogen content
  • a first possible source of error for determining the concentration of the hydrogen fraction in a sensor constructed in this way can be eliminated by providing a first oxygen ion pumping cell, preferably arranged close to the diffusion barrier in the sample gas sample chamber. This ensures the removal of existing in the sample gas, free oxygen molecules, which could otherwise enter into a measurement falsifying binding with hydrogen or would usually.
  • a first oxygen ion pumping cell preferably arranged close to the diffusion barrier in the sample gas sample chamber. This ensures the removal of existing in the sample gas, free oxygen molecules, which could otherwise enter into a measurement falsifying binding with hydrogen or would usually.
  • ceramic solid electrolyte is provided with two electrodes and acted upon by a corresponding electrical voltage.
  • a voltage source can be provided by means of which a pumping voltage (Up) can be applied at least during the measurement process between the two electrodes of the hydrogen ion pump.
  • This pumping voltage is preferably designed so that it is selectively parameterized for the splitting of the hydrogen-containing gas component, in particular NH 3 , into hydrogen (H) + one or more complementary components, such as nitrogen (N), at the first electrode.
  • the sample gas sample may preferably be parameterized so that it does not cause splitting of water (H 2 O) also present in the sample gas sample in the form of water vapor into oxygen (O) and hydrogen (H 2 ).
  • H 2 O water
  • O oxygen
  • H 2 hydrogen
  • Solid electrolyte of yttrium stabilized zirconia by means of the two associated with him two electrodes, inner and outer, are quantified by the resulting ion current or the corresponding electrode current exactly. But this again is an exact quantification of the complementary hydrogen ion current or the associated electron flow to the hydrogen ion pump possible.
  • the attached figure shows a schematic cross section through a gas sensor for determining a hydrogen-containing gas component and / or their concentration in a measurement gas, in particular for the determination of NH 3 .
  • the attached figure shows a schematic cross section through a gas sensor 1.
  • a proton conductor 2 which can be connected via two electrodes 3, 4 to a voltage source 5.
  • a diffusion barrier 8 is provided in order to separate a sample gas sample chamber 6 from a sensor region 7 to be exposed to the sample gas.
  • this diffusion barrier may have a selective filtering effect, so that only certain gas fractions can pass through it.
  • the electrode 3 arranged in the interior of the sample gas sample chamber 6 is preferably catalytically active with respect to a splitting of a hydrogen-containing gas component.
  • the proton conductor 2 is connected to the two electrodes 3, 4 as a hydrogen ion pumping cell 9.
  • Ceramic bodies (10, 11, 12), preferably yttrium-stabilized zirconia, are provided as carrier bodies for the sensor 1.
  • a heating element 13 is inside an insulation 14 embedded. By means of this heating element, the sensor can be adjusted to a specific operating temperature.
  • the hydrogen ion pumping cell 9 is arranged in the plane of the layer 11 together with the sample gas sample chamber 6 and the diffusion barrier 8.
  • the sensor region 7 to be exposed to the measurement gas is in this case designed, for example, in the end region of the sensor 1. Through it, the test gas to be tested can diffuse across the diffusion barrier 8 into the sample gas sample chamber 6.
  • an electric current flowing through the two electrodes 3, 4 is detected as a measure of the concentration of hydrogen ions of the gas component to be detected by the ammeter 15 shown here by way of example.
  • a first oxygen-ion pump cell for eliminating such measurement errors. It comprises the ceramic solid-state electrolyte 17 formed as a carrier element as well as the two electrodes 18, 19. The outer electrode 18 is additionally coated with a protective layer 20. For operation of the oxygen-ion pumping cell 16, a current or voltage source 21 is further provided.
  • the present invention therefore additionally proposes a second oxygen pumping cell 23 spatially or functionally associated with the sample gas sampling chamber. This is how the Oxygen Ionenpumpzelle 21, an inner electrode 23 and an outer electrode 24, which are conductively connected to each other by an electrolyte oxygen ions.
  • this oxygen-ion conducting electrolyte is again produced by the ceramic body in the form of a yttrium-stabilized zirconia, which is designed as a carrier body.
  • a protective layer 26 is also shown here by way of example.
  • the inner electrode 23 of the second oxygen-ion pumping cell 22 in the vicinity of the inner Electrode 3 of the hydrogen ion pumping cell 9 is arranged.
  • these two electrodes face each other in the sample gas sample chamber 6.
  • all the oxygen atoms released by the splitting of the water (H 2 O) into (2H) plus (O) can be quantified. This is done by means of the electrons of the corresponding electric current flowing through the amperometer 28 shown here by way of example.
  • the measurement error resulting from the splitting of water is known and can be reliably corrected by a corresponding subtraction on the measurement result of the hydrogen ion pump cell. What remains is only the hydrogen ion current, which results from the splitting of the measurement gas component to be detected, such as NH 3 .
  • the present invention further provides that the two inner electrodes 19, 23 of the two oxygen-ion pumping cells 16, 22 are constructed from materials which as far as possible do not split the water into Support or cause hydrogen and oxygen fractions. You can do this, for example, from a Blend of platinum (Pt) with about 0.5% gold (Au) or consist of a mixture of palladium (Pd) with about 5, 0% gold (Au).
  • the inner electrode 3 of the hydrogen ion pump cell can consist, for example, of pure platinum (Pt), which, as is known, has very good catalytic properties with regard to a splitting of hydrogen-containing gas components.
  • the proton conductor 2 may itself be composed of proportions of barium zirconate, in particular of doped barium zirconate. In the present example, this barium zirconate is embedded in an insulation 29 in the form of aluminum oxide (Al 2 O 3).

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Abstract

The present invention relates to a gas sensor (1) for determining a hydrogen-containing gas component and/or its concentration in a measurement gas, in particular for determining NH3, said sensor comprising two electrodes (3, 4) which are connected, such that they conduct protons, by means of a proton conductor (2), wherein a diffusion barrier (8) is arranged between a sensor region (7) which is to be exposed to the measurement gas and a first electrode (3) which is catalytically active with respect to cleaving of the hydrogen-containing gas component. The gas sensor is distinguished by the fact that the proton conductor (2) is connected to the two electrodes (3, 4) as a hydrogen ion pump cell (5, 15).

Description

Beschreibungdescription
Titeltitle
Gassensorgas sensor
Die vorliegende Erfindung betrifft einen Gassensor zur Bestimmung einer wasserstoffhaltigen Gaskomponente und/oder ihrer Konzentration in einem Messgas, nach dem Oberbegriff des Anspruchs 1.The present invention relates to a gas sensor for determining a hydrogen-containing gas component and / or its concentration in a measuring gas, according to the preamble of claim 1.
Stand der TechnikState of the art
Aus der EP 0 693 180 Bl ist ein Ammoniaksensor bekannt, der auf amperometrische Basis arbeitet, wobei eine für Ammoniak permeable Membran den Sensor zu einer Messgasprobe hin abschließt. Der Elektrolyt enthält ein von Luftsauerstoff in wässriger Lösung nicht oxidierbares Metall-Ion, das mit Ammoniak ein komplexes, mit Sauerstoff oxidierbares Metall-Ion bildet. Dieser Sensor ist für Raumtemperatur und/oder wässrige Lösungen ausgelegt. Sein Einsatzbereich ist dementsprechend eingeschränkt .EP 0 693 180 B1 discloses an ammonia sensor which operates on an amperometric basis, wherein a membrane permeable to ammonia seals off the sensor to form a sample gas sample. The electrolyte contains a metal ion which is not oxidizable by atmospheric oxygen in aqueous solution and which forms a complex, oxygen-oxidizable metal ion with ammonia. This sensor is designed for room temperature and / or aqueous solutions. Its field of application is accordingly limited.
Die WO 01/48466 A2 offenbart ein Sensorelement eines Gassensors zur Bestimmung der Konzentration von in einem Gasgemisch vorhandenem Wasserstoff oder von wasserstoff- haltigen Gaskomponenten wie Ammoniak oder Kohlenwasserstoffe. Dabei wird auf der Basis eines protonenleitenden Festkörperelektrolyten eine durch unterschiedliche Wasserstoff- bzw. Protonenkonzentration an zwei Mess- bzw. Referenzelektroden hervorgerufene EMK durch Messung der anliegenden elektrischen Spannung im sogenannten „Nernstzellen"-Betriebsmodus ermittelt . Aufgabe und Vorteile der vorliegenden ErfindungWO 01/48466 A2 discloses a sensor element of a gas sensor for determining the concentration of hydrogen present in a gas mixture or of hydrogen-containing gas components such as ammonia or hydrocarbons. In this case, on the basis of a proton-conducting solid electrolyte, an emf caused by different hydrogen or proton concentration at two measuring or reference electrodes is determined by measuring the applied electrical voltage in the so-called "Nernst cell" operating mode. Purpose and advantages of the present invention
Der vorliegenden Erfindung liegt die Aufgabe zu Grunde, einen Gassensor zur Bestimmung von wasserstoffhaltigen Gaskomponenten in einem Messgas, insbesondere von NH3 Anteilen, entsprechend der einleitend dargelegten Art zu verbessern.The present invention is based on the object to improve a gas sensor for the determination of hydrogen-containing gas components in a sample gas, in particular NH3 shares, according to the manner outlined in the introduction.
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 zur Bestimmung einer wasserstoffhaltigen Gaskomponente und/oder ihrer Konzentration in einem Messgas, insbesondere zur Bestimmung von NH3, umfassend zwei durch einen Protonenleiter Protonen leitend verbundene Elektroden, wobei zwischen einem dem Messgas auszusetzenden Sensorbereich und einer ersten, bezüglich einer Aufspaltung der wasserstoffhaltigen Gaskomponente katalytisch wirksamen Elektrode eine Diffusionsbarriere angeordnet ist. Der Gassensor zeichnet sich dadurch aus, dass der Protonenleiter mit den beiden Elektroden als Wasserstoffionen-Pumpzelle beschaltet ist.Accordingly, the invention relates to a gas sensor for determining a hydrogen-containing gas component and / or its concentration in a measurement gas, in particular for the determination of NH 3 , comprising two protons conductively connected by a proton conductor electrodes, wherein between a measurement gas auszusetzenden sensor area and a first, with respect to a Splitting the hydrogen-containing gas component catalytically active electrode is disposed a diffusion barrier. The gas sensor is characterized in that the proton conductor is connected to the two electrodes as a hydrogen ion pumping cell.
Unter einer Pumpzelle wird ein über zwei Elektroden kontaktierter, amperometrisch betriebener Elektrolyt verstanden. Das heißt, an den beiden Elektroden liegt eine Potentialdifferenz an, und der von der Ionenwanderung durch den Elektrolyten hervorgerufene elektrische Strom wird z. B. als Maß für die Konzentration an Wasserstoffanteilen im Messgas detektiert. Gleiches gilt selbstverständlich für einen Protonenleiter .A pump cell is understood as meaning an amperometrically operated electrolyte contacted via two electrodes. That is, at the two electrodes is a potential difference, and caused by the ion migration through the electrolyte electric current is z. B. detected as a measure of the concentration of hydrogen in the sample gas. The same applies of course to a proton conductor.
Mittels eines zwischen den beiden Elektroden fließenden elektrischen Stromes ist eine sehr genaue Quantisierung eines durch den Wasserstoff-Protonenleiter fließenden Wasserstoff- Ionen-Strom möglich und damit eine indirekte Bestimmung von NH3-Anteilen im Messgas.By means of an electric current flowing between the two electrodes, a very precise quantization of a hydrogen-ion current flowing through the hydrogen proton conductor is possible and thus an indirect determination of NH 3 content in the sample gas.
In einer möglichen Ausfuhrungsform kann der als Festkörper ausgebildete Wasserstoff-Protonenleiter aus Bariumzirkonat aufgebaut sein, insbesondere aus dotiertem Bariumzirkonat. Der Aufbau eines solchen Gassensors kann beispielsweise in der Form eines planaren Sensorelements erfolgen. Als Grundkeramik kann beispielsweise ein Yttrium-stabilisiertes ZirkonoxidIn one possible embodiment, the hydrogen proton conductor formed as a solid may be composed of barium zirconate, in particular of doped barium zirconate. The construction of such a gas sensor can be carried out, for example, in the form of a planar sensor element. As a basic ceramic, for example, an yttrium-stabilized zirconia
(YSZ) verwendet werden. Die Diffusionsbarriere dient als Gaswiderstand zwischen dem auf bestimmte Anteile und/oder Konzentrationen hin zu prüfenden Messgas und einer Messgasprobenkammer . Sie grenzt die Messgasprobenkammer gegenüber dem dem Messgas auszusetzenden Sensorbereich ab. Bei diesem Sensorbereich kann es sich z. B. um eine Öffnung an einer Seite des Sensors handeln.(YSZ). The diffusion barrier serves as a gas resistance between the sample gas to be tested for specific proportions and / or concentrations and a sample gas sample chamber. It delimits the sample gas sample chamber from the sensor area to be exposed to the sample gas. In this sensor area, it may be z. B. may be an opening on one side of the sensor.
Die aus den beiden Elektroden und dem Wasserstoff- Protonenleiter gebildete, sogenannte „Wasserstoffpumpe" pumpt den bei der Aufspaltung von Ammoniak (NH3) entstehenden Wasserstoff (H) in ionisierter Form (H+) aus der Messgasprobenkammer ab. In einer einfachen Ausfuhrungsform kann es beispielsweise wieder zurück in den Raum geschehen, in welchem sich das zu prüfende Messgas befindet. Denkbar wäre aber auch ein Abpumpen in einem von diesem Raum getrennten Bereich .The so-called "hydrogen pump" formed from the two electrodes and the hydrogen proton conductor pumps out the hydrogen (H) formed in the splitting of ammonia (NH 3 ) in ionized form (H + ) from the sample gas sample chamber For example, back to the room in which the sample gas to be tested is located, but it would also be conceivable to pump it off in an area which is separate from this room.
Zur Unterstützung der Aufspaltung des NH3 in seine Bestandteile wird weiterhin die Verwendung eines Katalysators vorgeschlagen, welcher insbesondere vorteilhaft in die in der Messgasprobenkammer angeordnete erste Innenelektrode integriert ist. Dazu kann diese erste Elektrode aus einem entsprechend geeigneten Material hergestellt sein, zum Beispiel aus Platin, insbesondere aus reinem Platin. Damit ist es möglich, den gesamten Wasserstoffanteil (H) der zu bestimmenden Gaskomponente, insbesondere von NH3 für die Auswertung des Messergebnisses in einen Wasserstoffionenstrom umzusetzen und durch die Erfassung des zwischen den beiden Elektroden fließenden elektrischen Stromes quantitativ zu bestimmen .To support the splitting of the NH 3 into its constituents, the use of a catalyst is furthermore proposed, which is particularly advantageously integrated into the first inner electrode arranged in the sample gas sample chamber. For this purpose, this first electrode may be made of a suitably suitable material, for example of platinum, in particular of pure platinum. Thus, it is possible to convert the total hydrogen content (H) of the gas component to be determined, in particular of NH3 for the evaluation of the measurement result into a hydrogen ion current and quantitatively by detecting the current flowing between the two electrodes electric current determine.
Eine erste mögliche Fehlerquelle für die Konzentrationsbestimmung des Wasserstoffanteiles bei einem derart aufgebauten Sensor kann dadurch ausgeschaltet werden, dass eine erste, vorzugsweise nahe der Diffusionsbarriere in der Messgasprobenkammer angeordnete Sauerstoffionen-Pumpzelle vorgesehen ist. Diese sorgt für den Abtransport von im Messgas vorhandenen, freien Sauerstoffmolekülen, die andernfalls eine das Messergebnis verfälschende Bindung mit Wasserstoff eingehen könnten bzw. in der Regel würden. Zum Abpumpen dieser Sauerstoffionen aus der Messgasprobenkammer kann z. B. der als Trägerkörper dienende, keramische Festkörperelektrolyt mit zwei Elektroden versehen und mit einer entsprechenden elektrischen Spannung beaufschlagt werden.A first possible source of error for determining the concentration of the hydrogen fraction in a sensor constructed in this way can be eliminated by providing a first oxygen ion pumping cell, preferably arranged close to the diffusion barrier in the sample gas sample chamber. This ensures the removal of existing in the sample gas, free oxygen molecules, which could otherwise enter into a measurement falsifying binding with hydrogen or would usually. For pumping out these oxygen ions from the sample gas sample chamber can, for. B. serving as a carrier body, ceramic solid electrolyte is provided with two electrodes and acted upon by a corresponding electrical voltage.
Zum Abpumpen des Wasserstoffionenstroms aus der Messgasprobenkammer kann demgegenüber eine Spannungsquelle vorgesehen sein, mittels der eine Pumpspannung (Up) zumindest während des Messvorgangs zwischen den beiden Elektroden der Wasserstoff-Ionenpumpe angelegt werden kann. Diese Pumpspannung ist dabei vorzugsweise so ausgelegt, dass sie selektiv für die Aufspaltung der wasserstoffhaltigen Gaskomponente, insbesondere NH3, in Wasserstoff (H) + eine oder mehrere komplementäre Komponenten, wie Stickstoff (N) , an der ersten Elektrode parametriert ist.For pumping the hydrogen ion stream out of the sample gas sample chamber, by contrast, a voltage source can be provided by means of which a pumping voltage (Up) can be applied at least during the measurement process between the two electrodes of the hydrogen ion pump. This pumping voltage is preferably designed so that it is selectively parameterized for the splitting of the hydrogen-containing gas component, in particular NH 3 , into hydrogen (H) + one or more complementary components, such as nitrogen (N), at the first electrode.
Weiterhin kann sie vorzugsweise so parametriert sein, dass sie keine Aufspaltung von ebenfalls in der Messgasprobe vorhandenem Wasser (H2O) in der Form von Wasserdampf in Sauerstoff (O) und Wasserstoff (H2) bewirkt. So können nämlich durch entsprechend geeignete Spannungswerte deutliche Reduzierungen andernfalls auftretender Messfehler bewirkt werden .Furthermore, it may preferably be parameterized so that it does not cause splitting of water (H 2 O) also present in the sample gas sample in the form of water vapor into oxygen (O) and hydrogen (H 2 ). Thus, by correspondingly suitable voltage values, significant reductions of otherwise occurring measurement errors can be effected.
Unabhängig von dieser Pumpspannung finden aber in der in der Messgasprobenkammer befindlichen Messgasprobe Aufspaltungen von vorhandenen Wasseranteilen (H2O) in (0+2H) statt. Insbesondere bei hohen Betriebstemperaturen des Gassensors, wie diese z. B. beim Einsatz in Abgasanlagen der Fall ist, können solche Reaktionen aufgrund der für eine optimale Wirkung der Wasserstoffpumpe gezielt ausgebildeten, katalytischen Wirkung der betreffenden Innenelektrode gehäuft auftreten. Die dabei aus dem Wasser (H2O) frei gesetzten Wasserstoffanteile (2H) wandern daher zwangsweise durch die Wasserstoffpumpe und verfälschen damit das Messergebnis durch entsprechende Betragserhöhung des zwischen den beiden Elektroden der Wasserstoffpumpe fließenden elektrischen Stroms .Regardless of this pumping voltage, however, in the sample gas sample chamber located in the sample gas sample splits of existing water (H 2 O) in (0 + 2H) instead. In particular, at high operating temperatures of the gas sensor, as this z. B. is the case when used in exhaust systems, such reactions may occur due to the targeted for optimum effect of the hydrogen pump, catalytic effect of the respective inner electrode heaped. The thereby released from the water (H 2 O) released hydrogen components (2H) therefore forcibly move through the hydrogen pump and thus distort the measurement result by increasing the corresponding amount of the current flowing between the two electrodes of the hydrogen pump electric current.
Zur Bereinigung solcher Messfehler kann auf Grund der lokal begrenzten räumlichen Ausdehnung der vom Wasser (H2O) abgespaltenen Sauerstoffanteile (O) in vorteilhafter Weise ebenfalls eine räumliche Zuordnung einer zweiten Sauerstoffpumpe zur Innenelektrode der Wasserstoffpumpe vorgesehen werden. Damit können diese durch die Aufspaltung des Wasser (H2O) frei werdenden Sauerstoffanteile (0) durch Abpumpen über den SauerstoffionenleitendenIn order to correct such measurement errors, due to the spatially limited spatial extent of the oxygen components (O) split off from the water (H 2 O), a spatial allocation of a second oxygen pump to the inner electrode of the hydrogen pump can advantageously also be provided. Thus, these by the splitting of the water (H 2 O) released oxygen fractions (0) by pumping over the Sauerstoffionenleitenden
Festkörperelektrolyten aus Yttrium stabilisierten Zirkonoxid mittels der beiden ihm zugeordneten zwei Elektroden, innere und äußere, durch den dadurch verursachten Ionenstrom bzw. den korrespondierenden Elektrodenstrom exakt quantifiziert werden. Damit ist aber wiederum eine exakte Quantifizierung des komplementären Wasserstoffionenstroms bzw. des damit verbundenen Elektronenstroms an der Wasserstoff-Ionenpumpe möglich.Solid electrolyte of yttrium stabilized zirconia by means of the two associated with him two electrodes, inner and outer, are quantified by the resulting ion current or the corresponding electrode current exactly. But this again is an exact quantification of the complementary hydrogen ion current or the associated electron flow to the hydrogen ion pump possible.
Durch Abzug des entsprechenden Elektronenstromanteils aus der Wasserzersetzung vom gesamten, von der Wasserstoffpumpe gemessenen Strom, bleibt damit nunmehr der vom Ammoniak (NH3) abgespaltene Anteil als doppelt bereinigtes und damit extrem genaues Messergebnis übrig. Dies gilt insbesondere, wenn die den beiden Sauerstoffpumpen zugeordneten Innenelektroden im Gegensatz zu der der Wasserstoffpumpe zugeordneten Innenelektrode nur geringe beziehungsweise sogar keine katalytischen Eigenschaften bezüglich einer Aufspaltung von NH3 aufweisen. Als Material können dazu beispielsweise eine Mischung aus Platin (Pt) mit etwa 0,5 %-Anteilen Gold (Au) oder auch aus einer Mischung aus Paladium (Pd) mit etwa 5 % Anteilen Gold (Au) ausgebildet sein.By deducting the corresponding proportion of electron current from the decomposition of water from the total, measured by the hydrogen pump current, so now the split off of ammonia (NH 3 ) share remains as a double-adjusted and thus extremely accurate measurement result. This applies in particular if, in contrast to the internal electrode assigned to the hydrogen pump, the internal electrodes assigned to the two oxygen pumps have only little or even no catalytic properties with regard to splitting NH 3 exhibit. For example, a mixture of platinum (Pt) with about 0.5% of gold (Au) or of a mixture of palladium (Pd) with about 5% of gold (Au) may be used as the material.
Ausführungsbeispielembodiment
Die Erfindung wird anhand der Zeichnung und der nachfolgend darauf bezugsnehmenden Beschreibung näher erläutert. Demnach zeigt die beigefügte Figur einen schematischen Querschnitt durch einen Gassensor zur Bestimmung einer wasserstoffhaltigen Gaskomponente und/oder ihrer Konzentration in einem Messgas, insbesondere zur Bestimmung von NH3.The invention will be explained in more detail with reference to the drawing and the description below. Accordingly, the attached figure shows a schematic cross section through a gas sensor for determining a hydrogen-containing gas component and / or their concentration in a measurement gas, in particular for the determination of NH 3 .
Im Detail zeigt die beigefügte Figur einen schematischen Querschnitt durch einen Gassensor 1. Zur Detektierung einer wasserstoffhaltigen Gaskomponente bzw. deren Konzentration ist er mit einem Protonenleiter 2 ausgestattet, welcher über zwei Elektroden 3, 4 an eine Spannungsquelle 5 angeschlossen werden kann. Zur Abtrennung einer Messgasprobenkammer 6 von einem dem Messgas auszusetzenden Sensorbereich 7 ist eine Diffusionsbarriere 8 vorgesehen. Sie stellt einen Gaswiderstand da, durch den das Messgas in die Messgasprobenkammer 6 hindurch diffundieren muss. Gegebenenfalls kann diese Diffusionsbarriere eine selektive Filterwirkung aufweisen, so dass nur bestimmte Gasanteile durch sie hindurch dringen können. Die im Inneren der Messgasprobenkammer 6 angeordnete Elektrode 3 ist vorzugsweise bezüglich einer Aufspaltung einer wasserstoffhaltigen Gaskomponente katalytisch wirksam. Erfindungsgemäß ist der Protonenleiter 2 mit den beiden Elektroden 3, 4 als Wasserstoff-Ionenpumpzelle 9 geschaltet.In detail, the attached figure shows a schematic cross section through a gas sensor 1. To detect a hydrogen-containing gas component or its concentration, it is equipped with a proton conductor 2, which can be connected via two electrodes 3, 4 to a voltage source 5. In order to separate a sample gas sample chamber 6 from a sensor region 7 to be exposed to the sample gas, a diffusion barrier 8 is provided. It provides a gas resistance through which the sample gas must diffuse into the sample gas sample chamber 6. Optionally, this diffusion barrier may have a selective filtering effect, so that only certain gas fractions can pass through it. The electrode 3 arranged in the interior of the sample gas sample chamber 6 is preferably catalytically active with respect to a splitting of a hydrogen-containing gas component. According to the invention, the proton conductor 2 is connected to the two electrodes 3, 4 as a hydrogen ion pumping cell 9.
Als Trägerkörper für den Sensor 1 sind Keramikschichten (10, 11, 12) vorzugsweise aus Yttrium stabilisierten Zirkonoxid, vorgesehen .Ceramic bodies (10, 11, 12), preferably yttrium-stabilized zirconia, are provided as carrier bodies for the sensor 1.
In der unteren Schicht 12 ist ein Heizelement 13 innerhalb einer Isolierung 14 eingebettet. Mittels dieses Heizelementes kann der Sensor auf eine bestimmte Betriebstemperatur eingestellt werden.In the lower layer 12, a heating element 13 is inside an insulation 14 embedded. By means of this heating element, the sensor can be adjusted to a specific operating temperature.
Die erfindungsgemäße Wasserstoff-Ionenpumpzelle 9 ist in der Ebene der Schicht 11 zusammen mit der Messgasprobenkammer 6 und der Diffusionsbarriere 8 angeordnet. Der dem Messgas auszusetzende Sensorbereich 7 ist hierbei beispielhaft im stirnseitigen Bereich des Sensor 1 ausgebildet. Durch ihn kann das zu prüfende Messgas über die Diffusionsbarriere 8 hinweg in die Messgasprobenkammer 6 eindiffundieren.The hydrogen ion pumping cell 9 according to the invention is arranged in the plane of the layer 11 together with the sample gas sample chamber 6 and the diffusion barrier 8. The sensor region 7 to be exposed to the measurement gas is in this case designed, for example, in the end region of the sensor 1. Through it, the test gas to be tested can diffuse across the diffusion barrier 8 into the sample gas sample chamber 6.
Ein durch die beiden Elektroden 3, 4 fließender elektrischer Strom wird erfindungsgemäß als Maß für die Konzentration an Wasserstoff-Ionen der zu detektierenden Gaskomponente durch das, hier beispielhaft dargestellte, Amperemeter 15 erfasst.According to the invention, an electric current flowing through the two electrodes 3, 4 is detected as a measure of the concentration of hydrogen ions of the gas component to be detected by the ammeter 15 shown here by way of example.
Da auf Grund von im Messgas vorhandenen Sauerstoffmolekülen ein Abwandern von an der katalytisch wirksamen Elektrode 3 auftretenden, freien Wasserstoff-Ionen das Messergebnis verfälschen würde, ist zur Eliminierung solcher Messfehler im Weiteren eine erste Sauerstoff-Ionenpumpzelle vorgesehen. Sie umfasst den als Trägerelement ausgebildeten keramischen Festkörperelektrolyten 17 sowie die beiden Elektroden 18, 19. Die äußere Elektrode 18 ist zusätzlich mit einer Schutzschicht 20 überzogen. Zum Betrieb der Sauerstoff-Ionenpumpzelle 16 ist weiterhin eine Strom- oder Spannungsquelle 21 vorgesehen.Since, due to oxygen molecules present in the measurement gas, a migration of free hydrogen ions occurring at the catalytically active electrode 3 would falsify the measurement result, a first oxygen-ion pump cell is provided for eliminating such measurement errors. It comprises the ceramic solid-state electrolyte 17 formed as a carrier element as well as the two electrodes 18, 19. The outer electrode 18 is additionally coated with a protective layer 20. For operation of the oxygen-ion pumping cell 16, a current or voltage source 21 is further provided.
Da in Messgasen, insbesondere in Abgasen, auch hohe Anteile von gasförmigem Wasser (H2O) vorhanden sind, würde eine Aufspaltung dieser Wasserteile in Wasserstoff (2H) und Sauerstoff (O) eine Verfälschung des Messergebnisses an der Wasserstoff-Ionenpumpzelle 9 durch zusätzlich detektierten Wasserstoffanteil in der Messgasprobenkammer 6 bewirken. Da sich diese Aufspaltungsvorgänge nicht zuverlässig vermeiden lassen, schlägt die vorliegende Erfindung daher zusätzlich eine zweite, der Messgasprobenkammer räumlich bzw. funktionell zugeordnete Sauerstoffpumpzelle 23 vor. Diese besteht, wie die Sauerstoff-Ionenpumpzelle 21, aus einer inneren Elektrode 23 und einer äußeren Elektrode 24, welche durch einen Elektrolyten Sauerstoffionen leitend miteinander verbunden sind. Hier in dieser bevorzugten Ausfuhrungsform ist dieser Sauerstoff-Ionen leitende Elektrolyt wiederum durch den als Tragerkorper ausgebildeten Keramikkorper in der Form eines Yttrium-stabilisierten Zirkonoxids hergestellt. Zum mechanischen und/oder auch chemischen Schutz der äußeren Elektrode 24 ist auch hierbei beispielhaft eine Schutzschicht 26 dargestellt.Since high levels of gaseous water (H 2 O) are also present in sample gases, in particular in exhaust gases, a splitting of these water parts into hydrogen (2H) and oxygen (O) would additionally falsify the measurement result at the hydrogen ion pump cell 9 Hydrogen content in the sample gas sample chamber 6 effect. Since these splitting processes can not be reliably avoided, the present invention therefore additionally proposes a second oxygen pumping cell 23 spatially or functionally associated with the sample gas sampling chamber. This is how the Oxygen Ionenpumpzelle 21, an inner electrode 23 and an outer electrode 24, which are conductively connected to each other by an electrolyte oxygen ions. Here, in this preferred embodiment, this oxygen-ion conducting electrolyte is again produced by the ceramic body in the form of a yttrium-stabilized zirconia, which is designed as a carrier body. For mechanical and / or chemical protection of the outer electrode 24, a protective layer 26 is also shown here by way of example.
Um Verfälschungen des Messergebnisses an der Wasserstoff- Ionenpumpzelle 9 auf Grund zusatzlich durch sie erfassten Wasserstoff-Ionen, die aus der Aufspaltung von im Messgas vorhandenen Wasser hervorgehen, zu vermeiden, ist die innere Elektrode 23 der zweiten Sauerstoff-Ionenpumpzelle 22 in der Nahe der inneren Elektrode 3 der Wasserstoff-Ionenpumpzelle 9 angeordnet. Hier im Ausfuhrungsbeispiel liegen sich diese beiden Elektroden in der Messgasprobenkammer 6 gegenüber. Dadurch können alle durch die Aufspaltung des Wassers (H2O) in (2H) plus (O) freigewordenen Sauerstoffatome quantifiziert erfasst werden. Dies erfolgt an Hand der durch das hier beispielhaft dargestellte Amperometer 28 fließenden Elektronen des entsprechenden elektrischen Stromes. Somit ist auch der durch die Aufspaltung von Wasser entstehende Messfehler bekannt und kann durch eine entsprechende Subtraktion am Messergebnis der Wasserstoff-Ionenpumpzelle zuverlässig korrigiert werden. Übrig bleibt lediglich der Wasserstoff- Ionenstrom, welcher aus der Aufspaltung der zu detektierenden Messgaskomponente, wie zum Beispiel NH3, herrührt.In order to avoid distortions of the measurement result at the hydrogen ion pump cell 9 due to additionally detected by them hydrogen ions resulting from the splitting of water present in the sample gas, the inner electrode 23 of the second oxygen-ion pumping cell 22 in the vicinity of the inner Electrode 3 of the hydrogen ion pumping cell 9 is arranged. Here in the exemplary embodiment, these two electrodes face each other in the sample gas sample chamber 6. As a result, all the oxygen atoms released by the splitting of the water (H 2 O) into (2H) plus (O) can be quantified. This is done by means of the electrons of the corresponding electric current flowing through the amperometer 28 shown here by way of example. Thus, the measurement error resulting from the splitting of water is known and can be reliably corrected by a corresponding subtraction on the measurement result of the hydrogen ion pump cell. What remains is only the hydrogen ion current, which results from the splitting of the measurement gas component to be detected, such as NH 3 .
Um bereits im Vorfeld der Messergebnisauswertung positiv auf das Messergebnis einwirken zu können, sieht die vorliegende Erfindung im Weiteren vor, dass die beiden inneren Elektroden 19, 23 der beiden Sauerstoff-Ionenpumpzellen 16, 22 aus Materialien aufgebaut sind, die möglichst keine Aufspaltung des Wassers in Wasserstoff- und Sauerstoffanteile unterstutzen bzw. verursachen. Sie können dazu beispielsweise aus einer Mischung aus Platin (Pt) mit etwa 0,5%-Anteile Gold (Au) bestehen oder aus einer Mischung aus Palladium (Pd) mit etwa 5, 0%-Anteilen Gold (Au).In order to be able to have a positive effect on the measurement result in advance of the measurement result evaluation, the present invention further provides that the two inner electrodes 19, 23 of the two oxygen-ion pumping cells 16, 22 are constructed from materials which as far as possible do not split the water into Support or cause hydrogen and oxygen fractions. You can do this, for example, from a Blend of platinum (Pt) with about 0.5% gold (Au) or consist of a mixture of palladium (Pd) with about 5, 0% gold (Au).
Die innere Elektrode 3 der Wasserstoff-Ionenpumpzelle kann demgegenüber beispielsweise aus reinem Platin (Pt) bestehen, welche bekannter weise sehr gute katalytische Eigenschaften bezüglich einer Aufspaltung wasserstoffhaltiger Gaskomponenten aufweist. Der Protonenleiter 2 kann selbst aus Anteilen aus Bariumzirkonat aufgebaut sein, insbesondere aus dotiertem Bariumzirkonat . Im vorliegenden Beispiel ist dieses Bariumzirkonat in eine Isolierung 29 in der Form von Aluminiumoxid (AI2O3) eingebettet. By contrast, the inner electrode 3 of the hydrogen ion pump cell can consist, for example, of pure platinum (Pt), which, as is known, has very good catalytic properties with regard to a splitting of hydrogen-containing gas components. The proton conductor 2 may itself be composed of proportions of barium zirconate, in particular of doped barium zirconate. In the present example, this barium zirconate is embedded in an insulation 29 in the form of aluminum oxide (Al 2 O 3).

Claims

Ansprüche claims
1. Gassensor (1) zur Bestimmung einer wasserstoffhaltigen Gaskomponente und/oder ihrer Konzentration in einem Messgas, insbesondere zur Bestimmung von NH3, umfassend zwei durch einen Protonenleiter (2) Protonen leitend verbundene Elektroden (3, 4), wobei zwischen einem dem Messgas auszusetzenden Sensorbereich (7) und einer ersten, bezüglich einer Aufspaltung der wasserstoffhaltigen Gaskomponente katalytisch wirksamen Elektrode (3) eine Diffusionsbarriere (8) angeordnet ist, dadurch gekennzeichnet, dass der Protonenleiter (2) mit den beiden Elektroden (3, 4) als Wasserstoffionen- Pumpzelle (9) beschaltet ist.1. A gas sensor (1) for determining a hydrogen-containing gas component and / or its concentration in a measurement gas, in particular for the determination of NH3, comprising two by a proton conductor (2) protons electrically connected electrodes (3, 4), wherein between an exposed to the measurement gas Sensor region (7) and a first, with respect to a decomposition of the hydrogen-containing gas component catalytically active electrode (3) a diffusion barrier (8) is arranged, characterized in that the proton conductor (2) with the two electrodes (3, 4) as a hydrogen ion pumping cell (9) is connected.
2. Gassensor nach Anspruch 1, dadurch gekennzeichnet, dass ein zwischen den beiden Elektroden (3, 4) fließender elektrischer Strom ein Maß für die Konzentration an Wasserstoffionen der zu detektierenden Gaskomponente ist.2. Gas sensor according to claim 1, characterized in that between the two electrodes (3, 4) flowing electric current is a measure of the concentration of hydrogen ions of the gas component to be detected.
3. Gassensor nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Diffusionsbarriere (8) eine Messgasprobenkammer3. Gas sensor according to claim 1 or 2, characterized in that the diffusion barrier (8) has a measuring gas sample chamber
(6) gegenüber dem dem Messgas auszusetzenden Sensorbereich (7) abgrenzt.(6) delimits from the sensor area (7) to be exposed to the measurement gas.
4. Gassensor nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, dass eine erste, der Messgasprobenkammer4. Gas sensor according to claim 1, 2 or 3, characterized in that a first, the sample gas sample chamber
(6) zugeordnete Sauerstoffionen-Pumpzelle (16) vorgesehen ist. (6) associated oxygen ion pumping cell (16) is provided.
5. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine zumindest während des Messvorganges an der Wasserstoffionen-Pumpzelle (9) anliegende elektrische Pumpspannung selektiv für die Aufspaltung der wasserstoffhaltigen Gaskomponente an der ersten Elektrode (3), insbesondere von NH3, in Wasserstoff (H) + eine oder mehrere komplementäre Komponenten, wie Stickstoff (N) parametriert ist.5. Gas sensor according to one of the preceding claims, characterized in that an at least during the measuring operation at the hydrogen ion pumping cell (9) applied electrical pumping voltage selectively for the splitting of the hydrogen-containing gas component at the first electrode (3), in particular NH3, in hydrogen (H) + one or more complementary components, such as nitrogen (N) is parametrized.
6. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine zweite, der Messgasprobenkammer6. Gas sensor according to one of the preceding claims, characterized in that a second, the sample gas sample chamber
(6) räumlich bzw. funktionell zugeordnete Sauerstoffionen-Pumpzelle (22) vorgesehen ist.(6) spatially or functionally associated oxygen ion pumping cell (22) is provided.
7. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine Elektrode (23) der zweiten Sauerstoffionen-Pumpzelle (22) in der Messgasprobenkammer (6) räumlich bzw. funktionell der ersten Elektrode (3) der Wasserstoffionen-Pumpzelle (7) zugeordnet angeordnet ist.7. Gas sensor according to one of the preceding claims, characterized in that an electrode (23) of the second oxygen ion pumping cell (22) in the Meßgasprobenkammer (6) spatially or functionally associated with the first electrode (3) of the hydrogen ion pumping cell (7) is arranged.
8. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass eine in der Messgasprobenkammer (6) angeordnete Elektrode (19, 23) der ersten und/oder der zweiten Sauerstoffionen-Pumpzelle (16, 22) aus einem Material mit geringen bis keinen katalytischen Eigenschaften bezüglich einer Aufspaltung von wasserstoffhaltigen Gaskomponenten ausgebildet ist.8. Gas sensor according to one of the preceding claims, characterized in that in the Meßgasprobenkammer (6) arranged electrode (19, 23) of the first and / or the second oxygen ion pumping cell (16, 22) of a material with little to no catalytic Characteristics with respect to a decomposition of hydrogen-containing gas components is formed.
9. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die Elektrode (19, 23) der ersten und/oder der zweiten Sauerstoffionen-Pumpzelle (16, 22) aus einer Mischung aus Platin (Pt) mit etwa 0, 5%-Anteilen Gold (Au) besteht, oder aus einer Mischung aus Palladium9. Gas sensor according to one of the preceding claims, characterized in that the electrode (19, 23) of the first and / or the second oxygen ion pumping cell (16, 22) of a mixture of platinum (Pt) with about 0, 5% - Shares of gold (Au) consists, or of a mixture of palladium
(Pd) mit etwa 5, 0%-Anteilen Gold (Au). (Pd) with about 5. 0% gold (Au).
10. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass der Wasserstoff- Protonenleiter (2) Anteile von Bariumzirkonat aufweist.10. Gas sensor according to one of the preceding claims, characterized in that the hydrogen proton conductor (2) comprises proportions of barium zirconate.
11. Gassensor nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass die erste Elektrode (3) aus Platin (Pt) hergestellt ist. 11. Gas sensor according to one of the preceding claims, characterized in that the first electrode (3) made of platinum (Pt) is prepared.
PCT/EP2007/050129 2006-02-22 2007-01-08 Gas sensor WO2007096203A1 (en)

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