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WO1996004550A1 - Detecteur de gaz electrochimique a sensibilite croisee reduite - Google Patents

Detecteur de gaz electrochimique a sensibilite croisee reduite Download PDF

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Publication number
WO1996004550A1
WO1996004550A1 PCT/CH1995/000166 CH9500166W WO9604550A1 WO 1996004550 A1 WO1996004550 A1 WO 1996004550A1 CH 9500166 W CH9500166 W CH 9500166W WO 9604550 A1 WO9604550 A1 WO 9604550A1
Authority
WO
WIPO (PCT)
Prior art keywords
gas sensor
electrode
sensor according
measuring
membrane
Prior art date
Application number
PCT/CH1995/000166
Other languages
German (de)
English (en)
Inventor
Christian Huggenberger
Original Assignee
Christian Huggenberger
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Christian Huggenberger filed Critical Christian Huggenberger
Priority to EP95924150A priority Critical patent/EP0721583A1/fr
Publication of WO1996004550A1 publication Critical patent/WO1996004550A1/fr

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Classifications

    • 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
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G01N27/4045—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for 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
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0011—Sample conditioning
    • G01N33/0014—Sample conditioning by eliminating a gas

Definitions

  • the invention relates to an electrochemical gas sensor, in particular for carbon monoxide and hydrogen, with reduced cross sensitivity according to the preamble of patent claim 1.
  • electrochemical gas sensors have proven themselves for the detection of toxic or explosive gases, the mode of operation of which is based on direct electrochemical oxidation or reduction of the gas to be measured.
  • the cell current maintained by gas diffusion is a function of the gas concentration and, to a good approximation, proves to be linear within the measuring range limits.
  • Such gas measuring cells are, however, cross-sensitive to certain interfering gases, which can lead to a falsification of the measured value, cf. e.g. W.Pauli, Chemistry - Environmental Technology, 1988/89, 62.
  • electrochemical gas sensors are offered which are equipped with a filter unit, usually integrated in the sensor housing, for removing interfering gases, such as H 2 S, S0 2 , NO, N0 2 .
  • a filter unit usually integrated in the sensor housing, for removing interfering gases, such as H 2 S, S0 2 , NO, N0 2 .
  • Suitable filter materials remove unwanted gases by adsorption, absorption or chemisorption.
  • the disadvantage of such filter units is that their capacity and thus their effectiveness decrease over time with continuous exposure and higher concentrations of interfering gases, which directly limits the range of use of the gas sensor when the filter unit is integrated, cf. see for example City Technology Ltd., London, Great Britain, Product Data Handbook 1992, in particular pp. 40, 66 - 68.
  • the filter capacity depends on the type of interfering gas. In the case of H 2 S, the capacity is exhausted very easily at concentrations well above the MAK value. moreover interfering gases such as H 2 cannot be filtered out in this way.
  • the interference signal can be reduced or eliminated by means of compensation devices, cf. e.g. EP 126 623 A2 and EP 127 387 A2.
  • the electrochemical gas sensor consists of a 2-electrode arrangement, whereby gas access is also guaranteed for the counter electrode. If a gas reacts incompletely at the measuring electrode, it can reach the counter electrode via a partially gas-permeable separator and can also react there. This results in partial compensation of the measuring current. In contrast, gases that react completely with the measuring electrode give a full measuring signal.
  • the principle of operation of multi-electrode sensors with auxiliary and reference electrodes, which are described in connection with corresponding electronic compensation circuits, is based on a similar principle.
  • EP 84935 B1 describes a similar device for the separate detection of CO in addition to H 2 , the different response times of the two gases being used.
  • the object of the present invention is to provide a simply constructed electrochemical-based gas sensor with reduced cross-sensitivity, which should have a long service life.
  • the selective membrane contains a catalyst wetted with electrolyte, which is electro- is catalytically inactive as much as possible, but is electrocatalytically as active as possible with regard to disruptive gases, so that these are converted, at a positive level, into products which are no longer disruptive or less disruptive.
  • the at least one porous catalyst layer of the selective membrane preferably consists of at least one fine-grained noble metal and polytetrafluoroethylene (PTFE) powder. Palladium, gold, platinum, ruthenium, iridium, osmium and / or silver in pure form, alloy or mixture are possible as noble metals.
  • the porous catalyst layer is preferably applied to a porous PTFE membrane and permanently connected to it by pressing or by sintering at a temperature T> 320 ° C. to form the selective membrane according to the invention.
  • a porous, partially hydrophobic / hydrophilic intermediate layer is applied directly to the selective membrane with a measuring electrode, which allows a particularly compact structure of the gas sensor, which is particularly suitable for determining C0 and H 2 .
  • the chemical reactions in the integrated selective membrane can be formulated in the presence of the interfering gases H 2 S, S0 2 or N0 2 and in the presence of a noble metal catalyst, such as palladium or gold, which is active in relation to these gases:
  • the catalyst layer of the selective membrane wetted with the electrolyte can to a certain extent be an intimate combination of a similar working and counter electrode electrical discharges to the outside are understood, the electrons of the redox reactions being exchanged internally in the catalyst layer instead of via an external conductor.
  • H 2 S and S0 2 only H 2 S0 4 is formed in the reaction balance, for example the electrolyte itself.
  • N0 2 NO is formed.
  • a CO measuring electrode, based on a platinum catalyst, is less sensitive to this, and theoretically a measuring current would be expected which has the sign of a reducing gas.
  • a weak signal is sometimes measured with the opposite sign, which indicates that in addition to NO there is also a residual concentration of N0 2 , which also reacts at the measuring electrode.
  • the electrode reactions can be formulated as follows:
  • Measuring electrode CO + H 2 0> C0 2 + 2 H * + 2 e
  • the electrical current generated can be measured with an intermediate ammeter and is a function of the CO concentration.
  • 1 shows a longitudinal section of an electrochemical gas sensor with the electrocatalytically selective membrane according to the invention
  • 2 shows a longitudinal section of a combination of the selective membrane according to the invention with a measuring electrode to form a selective membrane electrode
  • 3 is a top view of a combined reference and counter electrode
  • FIG. 4 shows a longitudinal section of a gas sensor with a selective membrane electrode according to the invention.
  • FIG. 5 shows a longitudinal section of a gas sensor with a separate selective membrane according to the invention.
  • the selective membrane 5a contains at least one electrically conductive, finely divided catalyst 5b, which is preferably wetted by the electrolyte 19a of the measuring cell 7 itself.
  • the selective membrane 5a is preferably closed off by a gas-permeable, porous membrane 3, which represents a barrier for the electrolyte 19a of the measuring cell 7.
  • the selective membrane 5a is separated from the measuring electrode 11a by a thin gap 24 containing electrolyte 19a.
  • Measuring and counter electrodes 11a, 12 are connected to an ammeter 22 via inert contact wires.
  • the catalyst 5b of the selective membrane 5a is designed in such a way that it is electrocatalytically inactive with regard to the gas to be detected (measurement gas), but is as active as possible with respect to other gases 18 that are interfering with one another.
  • the measuring gas 17 can pass through the porous, selective membrane 5a without undergoing an electrochemical reaction in order to reach the measuring electrode 11a via the gap 24.
  • the corresponding counter-reaction forms in the same selective membrane 5a with the internal exchange of electrons.
  • oxygen that is supplied from the environment is reduced to water at the same time.
  • oxygen is formed as a counter-reaction in the selective membrane 5a and is released into the environment. If the oxidation or reduction products of the interfering gases 18 are inert with respect to the catalyst of the measuring electrode 11a, the current measured between the measuring and counter electrodes 11a, 12 is generated solely by the measuring gas 17.
  • the electrocatalytically selective membrane 5a can be produced as follows: A porous PTFE (polytetrafluoroethylene) membrane 3 is preferably used as the base 3. A porous catalyst layer 5b, which consists of a mixture of finely divided noble metal catalyst and PTFE powder, can be applied to this. Fixation can be achieved by pressing or by sintering at T> 320 * C. Mixtures of several noble metal catalysts can also be used or the various catalysts can be applied in multiple layers.
  • a hydrophilic thin glass fiber filter 10 can be used as the gap material 24a for conveying the electrolyte 19a and for the spatial separation from the measuring electrode 11a. It is better to use a partially hydrophobic / hydrophilic membrane since this increases the diffusion flow of the measurement gas 17.
  • This can consist of a thin, porous and sintered membrane made of finely divided PTFE powder on the one hand and quartz powder or amorphous SiO 2 powder on the other hand.
  • the hydrophilic component eg fine quartz powder
  • PTFE forms paths for the sample gas 17.
  • Such a selective membrane electrode 5 can be produced as follows: A porous PTFE membrane 3 serves as a base. A porous catalyst layer 5b, consisting of a mixture of finely divided noble metal and PTFE powder, is applied to this. The layer 5b is covered with a porous intermediate layer 23, which consists of a mixture of finely divided PTFE powder and fine quartz powder or amorphous SiO 2 powder. Then the porous measuring electrode 11a, which consists of a mixture of finely divided noble metal and PTFE powder, is applied to the intermediate layer 23. For fixation, the layers can be pressed successively or simultaneously or sintered successively or simultaneously at T> 320 * C.
  • a gas sensor further comprises the following individual parts: fastening screws 1, acid-resistant plastic O-rings 4, unsintered PTFE strips 6, a central body 7a, preferably made of polycarbonate plastic, contact springs 8, made of a film, preferably of thickness Platinum tapes 9 cut 0.025 mm, tampons made of glass fiber filter material 10, an electrolyte chamber 19 partially filled with an electrolyte 19a with an opening 13 and a wick made of glass fiber filter material 10a for conveying the electrolyte to the electrodes 11a, 11, 12, a cover 14 , preferably made of polycarbonate plastic with a yoke for pressure compensation 20, bore 15 with thread for fastening screws 1, pressure compensation opening 20, preferably with a diameter of approx. 0.5 mm and a capillary length of approx. 5 mm.
  • a reference and counterelectrode 11, 12 according to FIG. 3 is produced as follows: a round glass fiber filter 10 is a catalyst layer separated by a gap 21, which contains a mixture of platinum black and PTFE powder, applied and then in the oven at T ⁇ 360 * C sintered.
  • the electrode is separated into a reference and a counter electrode 11, 12.
  • the sensor is mounted as shown in FIG. 4, and the housing parts
  • the electrolyte chamber 19 of the sensor is filled with 1.5 ml of aqueous sulfuric acid (30% by mass) and screwed to the cover 14.
  • a wick 10a made of glass fiber filter material lining the electrolyte chamber 19 is in contact through the opening 13 with the reference and counter electrodes 11, 12 for further transmission of the electrolyte to the tampon 10 and the electrodes 11, 12, 5.
  • the reference and counter electrodes 11, 12 are in intimate contact with a porous PTFE membrane 3, which always ensures the replenishment of atmospheric oxygen for the counter-reaction.
  • a conventional co-sensor is also produced for a comparison measurement of the cross-sensitivities: the measuring electrode is a conventional membrane electrode 16a.
  • the sensor is manufactured as described in the first example. In this sensor, too, the cross sensitivity to H 2 S, S0 2 and N0 2 is drastically reduced according to Table 1. The response time and sensitivity to CO is comparable to the first example. In contrast to the first example, a weakly positive signal is observed at N0 2 .
  • a selective sensor is produced, with the only difference that the selective membrane 5a contains platinum black instead of palladium black. Since platinum black has an electrocatalytic effect on CO, CO is already oxidized in the selective membrane. In contrast, according to Table 1, H 2 reacts incompletely in the selective membrane 5a, so that a relatively large part is perceived by the measuring electrode 11a.
  • a sensor according to example 3 can be used as an H 2 sensor.
  • a measuring gas 17 which is more difficult to oxidize can also be detected with a sensor according to Example 3.
  • the cross-sensitivity to the interference gases 18, which is normally increased by the bias voltage, can be drastically reduced in the presence of the selective membrane 5a.
  • a 2-electrode sensor is produced according to FIG. 5.
  • a thin glass fiber round filter 10 is used as a separator between the selective membrane 5a and the measuring electrode 16a.
  • 1.5 ml of sulfuric acid (30% by mass) are introduced as electrolyte 19a.
  • the measurement of CO and cross-sensitivities are carried out analogously to the 1st example.
  • the ammeter 22 is connected to the measuring and counter electrodes 11a, 12.
  • the cross sensitivity is drastically reduced in this embodiment.
  • the response time with regard to CO is significantly slower here.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
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  • Engineering & Computer Science (AREA)
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Abstract

Une membrane sélective (5a) permet de considérablement et durablement réduire, par voie électrocatalytique, la sensibilité croisée de capteurs de gaz électrochimiques (7) à des gaz parasites (18). Afin d'éliminer certains gaz parasites (18), on choisit un catalyseur adapté (5b), appliqué sur une membrane (8) perméable aux gaz, de sorte que ces gaz se transforment en produits auxquels l'électrode de mesure (11a) réagit moins ou ne réagit plus du tout. Cependant, le gaz à détecter (17) ne doit pas, si possible, commencer à réagir de sorte qu'il puisse réagir totalement sur l'électrode de mesure (11a). Les membranes sélectives de ce type peuvent être combinées de façon avantageuse à des électrodes à membrane. A la différence des filtres d'adsorption chimiques et d'adsorption classiques, les membranes (5a) opérant par voie catalytique ont une action prolongée et n'épuisent pas leur capacité, y compris en présence de concentrations largement supérieures aux concentrations maximales au poste de travail. Les détecteurs de gaz électrochimiques équipés de ce type de membranes sélectives (5a) fonctionnent avec un système électronique d'évaluation traditionnel (dans le plus simple des cas avec un ampèremètre (22) raccordé à l'électrode de mesure (11a) et à une contre-électrode (12)) et ne nécessitent pas de système électronique de compensation complexe.
PCT/CH1995/000166 1994-08-02 1995-07-19 Detecteur de gaz electrochimique a sensibilite croisee reduite WO1996004550A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP95924150A EP0721583A1 (fr) 1994-08-02 1995-07-19 Detecteur de gaz electrochimique a sensibilite croisee reduite

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH241694 1994-08-02
CH2416/94-0 1994-08-02

Publications (1)

Publication Number Publication Date
WO1996004550A1 true WO1996004550A1 (fr) 1996-02-15

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999053314A1 (fr) * 1998-04-14 1999-10-21 Ge Syprotec Inc. Dispositif et procede servant a controler un ou plusieurs gaz dans un fluide dielectrique
WO2005085824A1 (fr) * 2004-03-03 2005-09-15 Zellweger Analytics Ag Detecteur de gaz a electrolyte liquide comprenant un support d'electrode poreux rigide
US7179355B2 (en) 2002-02-19 2007-02-20 Alphasense Limited Electrochemical cell
CN102621205A (zh) * 2012-03-28 2012-08-01 华瑞科学仪器(上海)有限公司 硫化氢电化学传感器
CN113324896A (zh) * 2021-05-27 2021-08-31 国网陕西省电力公司西安供电公司 一种用于高压电缆阻水缓冲层电化学腐蚀研究的实验装置
CN113933357A (zh) * 2021-11-18 2022-01-14 北京化工大学 聚四氟乙烯膜在气体传感器中的应用、气体传感器用金属管帽、二氧化氮传感器
US11378569B2 (en) 2020-08-31 2022-07-05 Simple Labs, Inc. Smoke taint sensing device
CN115950922A (zh) * 2023-01-17 2023-04-11 湖南元芯传感科技有限责任公司 有源过滤器、半导体气体传感器及有源过滤器的制备方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2374419B (en) * 2001-03-09 2004-12-29 Zellweger Analytics Ltd Electrochemical gas sensor

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3470071A (en) * 1966-07-11 1969-09-30 Leesona Corp Method and apparatus for detecting gas
EP0064337A1 (fr) * 1981-04-30 1982-11-10 National Research Development Corporation Mesure du bioxyde de carbone
EP0126623A2 (fr) * 1983-05-19 1984-11-28 City Technology Limited Détecteur de gaz
DE3519435A1 (de) * 1985-05-30 1986-12-11 Siemens AG, 1000 Berlin und 8000 München Sensor fuer gasanalyse
EP0299779A2 (fr) * 1987-07-15 1989-01-18 Sri International Microcapteurs pour gaz et vapeurs à temps de réponse rapide
US5296196A (en) * 1991-02-04 1994-03-22 Toyota Jidosha Kabushiki Kaisha Semiconductor hydrocarbon sensor

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3470071A (en) * 1966-07-11 1969-09-30 Leesona Corp Method and apparatus for detecting gas
EP0064337A1 (fr) * 1981-04-30 1982-11-10 National Research Development Corporation Mesure du bioxyde de carbone
EP0126623A2 (fr) * 1983-05-19 1984-11-28 City Technology Limited Détecteur de gaz
DE3519435A1 (de) * 1985-05-30 1986-12-11 Siemens AG, 1000 Berlin und 8000 München Sensor fuer gasanalyse
EP0299779A2 (fr) * 1987-07-15 1989-01-18 Sri International Microcapteurs pour gaz et vapeurs à temps de réponse rapide
US5296196A (en) * 1991-02-04 1994-03-22 Toyota Jidosha Kabushiki Kaisha Semiconductor hydrocarbon sensor

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999053314A1 (fr) * 1998-04-14 1999-10-21 Ge Syprotec Inc. Dispositif et procede servant a controler un ou plusieurs gaz dans un fluide dielectrique
US7179355B2 (en) 2002-02-19 2007-02-20 Alphasense Limited Electrochemical cell
WO2005085824A1 (fr) * 2004-03-03 2005-09-15 Zellweger Analytics Ag Detecteur de gaz a electrolyte liquide comprenant un support d'electrode poreux rigide
US8303788B2 (en) 2004-03-03 2012-11-06 Honeywell Analytics Ag Liquid electrolyte gas sensor comprising rigid porous electrode support
CN102621205A (zh) * 2012-03-28 2012-08-01 华瑞科学仪器(上海)有限公司 硫化氢电化学传感器
US11378569B2 (en) 2020-08-31 2022-07-05 Simple Labs, Inc. Smoke taint sensing device
CN113324896A (zh) * 2021-05-27 2021-08-31 国网陕西省电力公司西安供电公司 一种用于高压电缆阻水缓冲层电化学腐蚀研究的实验装置
CN113933357A (zh) * 2021-11-18 2022-01-14 北京化工大学 聚四氟乙烯膜在气体传感器中的应用、气体传感器用金属管帽、二氧化氮传感器
CN115950922A (zh) * 2023-01-17 2023-04-11 湖南元芯传感科技有限责任公司 有源过滤器、半导体气体传感器及有源过滤器的制备方法

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Publication number Publication date
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