CA1096441A - Electrochemical cell having enhanced-surface non- conducting solid electrolyte and method of making same - Google Patents
Electrochemical cell having enhanced-surface non- conducting solid electrolyte and method of making sameInfo
- Publication number
- CA1096441A CA1096441A CA293,041A CA293041A CA1096441A CA 1096441 A CA1096441 A CA 1096441A CA 293041 A CA293041 A CA 293041A CA 1096441 A CA1096441 A CA 1096441A
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- Prior art keywords
- electrolyte
- porous
- electrochemical cell
- coating
- dense
- Prior art date
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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
-
- 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
- G01N27/4071—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
- H01M8/1231—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte with both reactants being gaseous or vaporised
-
- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
-
- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Electrochemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Pathology (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Molecular Biology (AREA)
- Manufacturing & Machinery (AREA)
- Engineering & Computer Science (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- General Chemical & Material Sciences (AREA)
- Measuring Oxygen Concentration In Cells (AREA)
- Fuel Cell (AREA)
- Conductive Materials (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Inert Electrodes (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
Abstract
ELECTROCHEMICAL CELL HAVING ENHANCED-SURFACE NON-CONDUCTING SOLID ELECTROLYTE
AND METHOD OF MAKING SAME
ABSTRACT
A layer of porous ion-conducting solid electrolyte material is applied to a dense substrate of the same material and then coated with a catalytic electrode to provide additional surface area in ionic continuity with the conduction paths for ion transport in the bulk lattice. For a yttria stabilized zirconia electrolyte, the enhanced surface area results in an oxygen sensing cell of a particular dimension having a much lower output impedance than a similarly dimensioned cell having only a dense electrolyte. Furthermore, the improved cell can operate at much lower temperatures than prior art cells. The catalytically coated porous high surface area electrolyte coating provides, in an automotive oxygen sensor, a dual function. Firstly, it provides a catalyst support in its outer extremities to provide thermodynamic equilibrium to the exhaust gases.
Secondly, it provides reactivity deep in the matrix of the coating between oxygen ions and the thermodynamically equilibrated gases. Further, a method is disclosed for lowering the output impedance of an electrochemical cell having a dense substrate of an ion-conducting solid electrolyte which is of a predetermined thickness. The invention would also be useful for fuel cells.
AND METHOD OF MAKING SAME
ABSTRACT
A layer of porous ion-conducting solid electrolyte material is applied to a dense substrate of the same material and then coated with a catalytic electrode to provide additional surface area in ionic continuity with the conduction paths for ion transport in the bulk lattice. For a yttria stabilized zirconia electrolyte, the enhanced surface area results in an oxygen sensing cell of a particular dimension having a much lower output impedance than a similarly dimensioned cell having only a dense electrolyte. Furthermore, the improved cell can operate at much lower temperatures than prior art cells. The catalytically coated porous high surface area electrolyte coating provides, in an automotive oxygen sensor, a dual function. Firstly, it provides a catalyst support in its outer extremities to provide thermodynamic equilibrium to the exhaust gases.
Secondly, it provides reactivity deep in the matrix of the coating between oxygen ions and the thermodynamically equilibrated gases. Further, a method is disclosed for lowering the output impedance of an electrochemical cell having a dense substrate of an ion-conducting solid electrolyte which is of a predetermined thickness. The invention would also be useful for fuel cells.
Description
4~
~; ~
'',~ ~ . ' . , ~
:, ELECTROCHEMICAL CELL HAVING ENHANCED- :
! SURFACE NCN~CONDUCTING SOLID ELECTR0~YTE
, AND METHOD OF MAKING SAME
.1 ~
BACKGROUND OF THE INVENTION
:~ This invention relates to elec~rcchemical cells such as oxygen sensors and ~uel ce:~ls bu~ particularly to oxygen sensing cells which in-corporate an oxygen^ion conducting solid elec~rolya~e such as yt~ria sta-bilized zirconia. Such cells are good ionlc conductors ancl are used to ',~ : ' i ! ` - 2 l .
genera~e a voltage signal in accordance with the familiar Nernst equation in response to diFferences in the partial pressures of oxygen on a ref-erence side (usually air~ and a sens;ng side.
As discussed at length ;n U.S. Patent :3,935,0~9, a convent~onal oxygen sensin~ cell having Pt electrodes depos;ted on either side of a stabilized oxygen-ion conducting solid electrolyte will experience a rather mild zhang~ i~ EMF as the engine air~fuel ratio (A/F) is varied about th~
stoichiome~ric ra-tio (S) ra~her than the sharp step change predicted by the Nernst equation. The mild transition is presumed ~o be oaused by the fact that oxidation reactions in an engine do not attain equlllbrium, so that oXygen concentra~ion in the exhaust gas is always higher than the theoretical value (the value predicted by the Nernst equation~ when an A/F lower than S (rich mixture) is employed. The P~ electrade in the exhaust gas acts as a catalyst ~or reactions of oxygen in the exhaust gas with unburned hydrocarbons and carbon monoxide but the catalytic effect ~ is insufficient to allow the reactions to obtain equilibrium~ The afore~
:~ mentioned patent proposes that a much sharper EMF transition can be made . as the A/F passes through S. This is accomplished by extending the elec trode surface by applying a coating of A1~03 to it which is ~mpregnated with a catalyst.
Although the aforementioned patent teach@s a way to increase the I surface area of the electrode to better achieve equilibrium of the gases9 .. ¦ the cell of the patent would necessarily still have a relatively high in-ternal impedance due to the relatively small surface area of the solid elec~roly~e, even after sandblasting. This is so since the oxygen ions are only conduc~ed ~hrough the zirconia electrolyte material. Where solid electrolyte cells are used to sense the oxygen content of an automotive .
'.
engine's exhaus-t ~as they must necessarily be quite compact so they can be insertecl in the fashion of a spark plug in-to the side oF an exhaust pipe. Typically, the solid electrolyte is in the Form of a stabilized zirconia wa~er ar a thimble which must have a suFficient thickness to pro-vide the strength necessary to resist damage in the rugged exhaust environ~ment. Unfortunately, the relatively small si~e of the cell and its rela-tively ~reat thickness combine -to provide the cell ~,~ith a substantial internal impedance. To maximize output, such cells are usually operated at relatively high temperatures, about 540 C., even though such high temperatures enhance the degradation of the catalys~ elec~rode. Obviously;
it would be desirable to be a~le to decrease the internal impedance of such cells to increase their voltage output and/or to permit operation at lower temperatures to provide increased life.
~-~ SUMMARY
It is among the objects of the present invention to provide an improved electrochemical cell and a method of making cells having a sig~
nificantly lower internal impedance than prior art cells oF the same thick-ness. It is another object of the invention to prov~de an electrochemical cell which can opera~e at lower temperatures than prior art cells of the same thickness.
According to the present invention, a porous stabilized zirconia network is fired onto the surface of a dense stabilized zirconia substrate such as a wafer or disc or a ~himble and a porous electrode coating is then
~; ~
'',~ ~ . ' . , ~
:, ELECTROCHEMICAL CELL HAVING ENHANCED- :
! SURFACE NCN~CONDUCTING SOLID ELECTR0~YTE
, AND METHOD OF MAKING SAME
.1 ~
BACKGROUND OF THE INVENTION
:~ This invention relates to elec~rcchemical cells such as oxygen sensors and ~uel ce:~ls bu~ particularly to oxygen sensing cells which in-corporate an oxygen^ion conducting solid elec~rolya~e such as yt~ria sta-bilized zirconia. Such cells are good ionlc conductors ancl are used to ',~ : ' i ! ` - 2 l .
genera~e a voltage signal in accordance with the familiar Nernst equation in response to diFferences in the partial pressures of oxygen on a ref-erence side (usually air~ and a sens;ng side.
As discussed at length ;n U.S. Patent :3,935,0~9, a convent~onal oxygen sensin~ cell having Pt electrodes depos;ted on either side of a stabilized oxygen-ion conducting solid electrolyte will experience a rather mild zhang~ i~ EMF as the engine air~fuel ratio (A/F) is varied about th~
stoichiome~ric ra-tio (S) ra~her than the sharp step change predicted by the Nernst equation. The mild transition is presumed ~o be oaused by the fact that oxidation reactions in an engine do not attain equlllbrium, so that oXygen concentra~ion in the exhaust gas is always higher than the theoretical value (the value predicted by the Nernst equation~ when an A/F lower than S (rich mixture) is employed. The P~ electrade in the exhaust gas acts as a catalyst ~or reactions of oxygen in the exhaust gas with unburned hydrocarbons and carbon monoxide but the catalytic effect ~ is insufficient to allow the reactions to obtain equilibrium~ The afore~
:~ mentioned patent proposes that a much sharper EMF transition can be made . as the A/F passes through S. This is accomplished by extending the elec trode surface by applying a coating of A1~03 to it which is ~mpregnated with a catalyst.
Although the aforementioned patent teach@s a way to increase the I surface area of the electrode to better achieve equilibrium of the gases9 .. ¦ the cell of the patent would necessarily still have a relatively high in-ternal impedance due to the relatively small surface area of the solid elec~roly~e, even after sandblasting. This is so since the oxygen ions are only conduc~ed ~hrough the zirconia electrolyte material. Where solid electrolyte cells are used to sense the oxygen content of an automotive .
'.
engine's exhaus-t ~as they must necessarily be quite compact so they can be insertecl in the fashion of a spark plug in-to the side oF an exhaust pipe. Typically, the solid electrolyte is in the Form of a stabilized zirconia wa~er ar a thimble which must have a suFficient thickness to pro-vide the strength necessary to resist damage in the rugged exhaust environ~ment. Unfortunately, the relatively small si~e of the cell and its rela-tively ~reat thickness combine -to provide the cell ~,~ith a substantial internal impedance. To maximize output, such cells are usually operated at relatively high temperatures, about 540 C., even though such high temperatures enhance the degradation of the catalys~ elec~rode. Obviously;
it would be desirable to be a~le to decrease the internal impedance of such cells to increase their voltage output and/or to permit operation at lower temperatures to provide increased life.
~-~ SUMMARY
It is among the objects of the present invention to provide an improved electrochemical cell and a method of making cells having a sig~
nificantly lower internal impedance than prior art cells oF the same thick-ness. It is another object of the invention to prov~de an electrochemical cell which can opera~e at lower temperatures than prior art cells of the same thickness.
According to the present invention, a porous stabilized zirconia network is fired onto the surface of a dense stabilized zirconia substrate such as a wafer or disc or a ~himble and a porous electrode coating is then
2~ applied. Unlike the non ion-conductive alumina coating proposed by Patent , 3,93~,089, the.porous y~.~ria-zirconia coating is an integral part of the I solid electroly~e matrix and as cuch provides a very large surface area for :1 ionic conduction at the gas-solid interfaces as compared to the area of the dense yttria-zirconia substrate. The large surface area, which is at leas-t 50-lOOOtimes the area oF the underlying substrate, serves to reduce or eliminate polarizations that can develop at the sensing surface since it provides many more 3-phase sites (p1atinum, z-irconia, and gas phase) where oxygen ions can pass through the surface and react wi~h C0 to Form C02. Since diPfusional processes limit the removal of rea~tion products, C2 tends to form an immobili7ed film over the surFace which restricts the access of the C0 to the oXygen ions at the 3-phase si~es. It is ob~
vious that the more sites there are for the oxygen ions to react with the C0, the greater will be the extent of the reaction. O~viously, the larger surface area for ion "transduction" (ionic transfer ~o and from the gas phase just across the gas-solid interface) dènotes a lowered impedance and the possibility for an increased flow of current as compared to a ce71 not havin~ an extended ion conduc~ive surface. The lowered tmpedance per mits lower temperature operation as compared to prior art cells for a given voltage signal. Thus~ the improved cell can begin producing signals sooner after engine startup or, alternatively, could be positioned further down-stream from the exhaust manifold than present devices where it could be expected to provide a lon~er life ~ue ~o the less rugged nature of the environment.
Preferably, a porous yttria-~irconia extension of the dense solid electrolyte matrix is provide~ on the referenee~gas side of the oxygen sensor in addition to that described above. This further minimizes the development of a polarizing potential within the solid electroly~e by providing more sites for oxygen ingress to the solid electrolyt~ matrix to accommodate ~he higher total flux of 0 ions as demartd2d by the external circuit on the new and improved low impedance device of this invention~
~g~
` Tile pre~erred embodiment oE the invention takes advantage oE the fact that a thlnner section of the clense electrolyte will by design have a lower intrinsic impedance. In this embodiment, recesses are formed in the central area oE both sides of a disc- or ~afer-shaped electrolyte. The hoop strength of the material surrounding the recesses minimizes the wea~cening of the structure produced by the recesses. By utiliæing the extended surface 7irconia coating~ the eEfective surface area for transduction can still be much greater than not only the projected surface areas of the recesses, but greater than the entire surface area of a disc not having recesses or a zirconia -~
coating.
In one particular aspect the present invention provides an electrochemical cell comprising a dense, non-porous self-supporting solid oxygen ion-conducting electrolyte member, a porous layer of less dense solid oxygen ion-conducting electrolyte in intimate contact with at least one surface of said m~mber, and a porous catalytic electrode on at least portions of said porous layer, said porous layer having a surf~ce area exposed to said electrode which exceeds the - surface area of the dense electrolyte member which it overlies by a factor of at least 50.
In another particular aspect the present invention provides a method of lowering the output impedance of an electrochemical cell having a dense substrate of an ion-conducting solid electrolyte material of a predetermined thickness: comprising the steps of coating at least a portion of one surface of the substrate with a coating of very fine particles of R porous ion-conducting solid electrolyte of the same chemical composition as said dense substrate; applying current collectors to each side of said substrate; and applying a catalyst containing solution to at :least portions Or sald - coating to catalytically activate said coating, said current jl/ -6-~ollectors and catalytically activated coatlng belng in electrically conduct:lng L-elat:Lonshlp and the surface area of said coating being at least 50 times greater than the sur:Eace area oE the substrate to which it is appl:Led.
In a fllrtller particular aspect the present invention provides an oxygen sensor for sensing the diEference in oxygen content between an exhaust gas from a combustion process and a reference gas, sai.d sensor including a body member and an oxygen ion-conductive me~ber of dense non--porous stabiliæed zirconia sealed in said bocly so one side is exposed to said exhaust gas and the other to said reference gas, one end of said zirconia member being coated on at least a portion of the surface thereof which is adapted to be exposed -. to all exhaust gas with a porous thick film coating of stabilized zirconla, a porous catalytic electrode in contact with the exposed surface of said coating, and current collectors in contact ~ith the opposite sides of said zirconia member, said porous thick film coating having a surface area exposecl to said electrode which exceeds the surface area of the dense zirconia member which it overlies by a factor of at least 50.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a fragmentary cross-section on line 1-1 of Figure 2 showing one embodiment of an oxygen sensor incorpor-ating the invention;
Figure 2 is an end view of the sensor of Figure l;
.~ Figure 3 is a fragmentary cross-section of an oxygen sensor incorporating a preferred embodiment of the invention;
Figure 4 is a cross-section of a recessed surface solid electrolyte having an artificlal macropore matrix;
Figure 5 is a photomicrograph o:E a 125~ thi.ck layer oE
porous zirconia on a zirconia substrate;
: Figure 6 is a graph plotting the ou~put voltage of a jl/ ~6a-,.~
-~ ~ell of this invention as a funct:ion of increaslng ~/F ratio and operating te~peratures;
Figure 7 is a graph plotting int~rnal cell resistance versus A/F for cells which do and do not have porous zirconia coatings under different temperature and f].ow condit:Lons; and ~ ' . ; ~ .
,- .
~ 20 `' ~
`' ;~` ' ~ :
6b-i r~i , Fi.gure 8 :ls a cross-sectlo~ of a fllel cell hav:i.l~g very large art:LEi.cia:l maclopores for pump:l.ng f~el or gas to the cell.
~ _) TA LhD _ES RI~TION 01~ 'LHE [NV.ENTION
Referr:;n~ to Figure 1., a fragmentary porti.on of an ; oxygen sens:in~ cell 10 :i9 shown w:Lth ~he climensi.o~s e~aggerated for clar;.ty. A waEer or disc 12 of den~;e, yttria stabilized zirconia is hermetical:ly sealed by a glass frit 13 in a recess 14 in the end o:E a non-ion conducting ceramic insulating tube 16 made o:E a material such as forsterite. The tube 16 could be of a short length, or it could be of the more conventional longer .
length designed to extend well into the exhaust gas stream.
A layer or coating 18 of porous stabilized zirconia of the same chemical composition as the dense zirconia ~ . substrate 12 overlies the substrate and defines an extended : ion-conducting surface Eor the substrate of at least 50-1000 :~ times the area of the substrate. A platinum collector ring 20 surrounds the extended layer 18 and stripes 22 of platinum are deposited on top of layer 18 and joined to the ring .20.
A lead 24 of platinum also joins the ring 20 with a jumper portion 24' and runs down the exterior surface of the tube 16 where it is available for connection into an electrical circuit (not shown).
Although not as much improvement is derived from providing an extended ion-conductive porous stabilized zirconia :layer 28 on the reference side of the sensor or :.~ cell 10 as on the sensing side, a significant improvement is provided which makes such layer 28 desirable.
~ 7
vious that the more sites there are for the oxygen ions to react with the C0, the greater will be the extent of the reaction. O~viously, the larger surface area for ion "transduction" (ionic transfer ~o and from the gas phase just across the gas-solid interface) dènotes a lowered impedance and the possibility for an increased flow of current as compared to a ce71 not havin~ an extended ion conduc~ive surface. The lowered tmpedance per mits lower temperature operation as compared to prior art cells for a given voltage signal. Thus~ the improved cell can begin producing signals sooner after engine startup or, alternatively, could be positioned further down-stream from the exhaust manifold than present devices where it could be expected to provide a lon~er life ~ue ~o the less rugged nature of the environment.
Preferably, a porous yttria-~irconia extension of the dense solid electrolyte matrix is provide~ on the referenee~gas side of the oxygen sensor in addition to that described above. This further minimizes the development of a polarizing potential within the solid electroly~e by providing more sites for oxygen ingress to the solid electrolyt~ matrix to accommodate ~he higher total flux of 0 ions as demartd2d by the external circuit on the new and improved low impedance device of this invention~
~g~
` Tile pre~erred embodiment oE the invention takes advantage oE the fact that a thlnner section of the clense electrolyte will by design have a lower intrinsic impedance. In this embodiment, recesses are formed in the central area oE both sides of a disc- or ~afer-shaped electrolyte. The hoop strength of the material surrounding the recesses minimizes the wea~cening of the structure produced by the recesses. By utiliæing the extended surface 7irconia coating~ the eEfective surface area for transduction can still be much greater than not only the projected surface areas of the recesses, but greater than the entire surface area of a disc not having recesses or a zirconia -~
coating.
In one particular aspect the present invention provides an electrochemical cell comprising a dense, non-porous self-supporting solid oxygen ion-conducting electrolyte member, a porous layer of less dense solid oxygen ion-conducting electrolyte in intimate contact with at least one surface of said m~mber, and a porous catalytic electrode on at least portions of said porous layer, said porous layer having a surf~ce area exposed to said electrode which exceeds the - surface area of the dense electrolyte member which it overlies by a factor of at least 50.
In another particular aspect the present invention provides a method of lowering the output impedance of an electrochemical cell having a dense substrate of an ion-conducting solid electrolyte material of a predetermined thickness: comprising the steps of coating at least a portion of one surface of the substrate with a coating of very fine particles of R porous ion-conducting solid electrolyte of the same chemical composition as said dense substrate; applying current collectors to each side of said substrate; and applying a catalyst containing solution to at :least portions Or sald - coating to catalytically activate said coating, said current jl/ -6-~ollectors and catalytically activated coatlng belng in electrically conduct:lng L-elat:Lonshlp and the surface area of said coating being at least 50 times greater than the sur:Eace area oE the substrate to which it is appl:Led.
In a fllrtller particular aspect the present invention provides an oxygen sensor for sensing the diEference in oxygen content between an exhaust gas from a combustion process and a reference gas, sai.d sensor including a body member and an oxygen ion-conductive me~ber of dense non--porous stabiliæed zirconia sealed in said bocly so one side is exposed to said exhaust gas and the other to said reference gas, one end of said zirconia member being coated on at least a portion of the surface thereof which is adapted to be exposed -. to all exhaust gas with a porous thick film coating of stabilized zirconla, a porous catalytic electrode in contact with the exposed surface of said coating, and current collectors in contact ~ith the opposite sides of said zirconia member, said porous thick film coating having a surface area exposecl to said electrode which exceeds the surface area of the dense zirconia member which it overlies by a factor of at least 50.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a fragmentary cross-section on line 1-1 of Figure 2 showing one embodiment of an oxygen sensor incorpor-ating the invention;
Figure 2 is an end view of the sensor of Figure l;
.~ Figure 3 is a fragmentary cross-section of an oxygen sensor incorporating a preferred embodiment of the invention;
Figure 4 is a cross-section of a recessed surface solid electrolyte having an artificlal macropore matrix;
Figure 5 is a photomicrograph o:E a 125~ thi.ck layer oE
porous zirconia on a zirconia substrate;
: Figure 6 is a graph plotting the ou~put voltage of a jl/ ~6a-,.~
-~ ~ell of this invention as a funct:ion of increaslng ~/F ratio and operating te~peratures;
Figure 7 is a graph plotting int~rnal cell resistance versus A/F for cells which do and do not have porous zirconia coatings under different temperature and f].ow condit:Lons; and ~ ' . ; ~ .
,- .
~ 20 `' ~
`' ;~` ' ~ :
6b-i r~i , Fi.gure 8 :ls a cross-sectlo~ of a fllel cell hav:i.l~g very large art:LEi.cia:l maclopores for pump:l.ng f~el or gas to the cell.
~ _) TA LhD _ES RI~TION 01~ 'LHE [NV.ENTION
Referr:;n~ to Figure 1., a fragmentary porti.on of an ; oxygen sens:in~ cell 10 :i9 shown w:Lth ~he climensi.o~s e~aggerated for clar;.ty. A waEer or disc 12 of den~;e, yttria stabilized zirconia is hermetical:ly sealed by a glass frit 13 in a recess 14 in the end o:E a non-ion conducting ceramic insulating tube 16 made o:E a material such as forsterite. The tube 16 could be of a short length, or it could be of the more conventional longer .
length designed to extend well into the exhaust gas stream.
A layer or coating 18 of porous stabilized zirconia of the same chemical composition as the dense zirconia ~ . substrate 12 overlies the substrate and defines an extended : ion-conducting surface Eor the substrate of at least 50-1000 :~ times the area of the substrate. A platinum collector ring 20 surrounds the extended layer 18 and stripes 22 of platinum are deposited on top of layer 18 and joined to the ring .20.
A lead 24 of platinum also joins the ring 20 with a jumper portion 24' and runs down the exterior surface of the tube 16 where it is available for connection into an electrical circuit (not shown).
Although not as much improvement is derived from providing an extended ion-conductive porous stabilized zirconia :layer 28 on the reference side of the sensor or :.~ cell 10 as on the sensing side, a significant improvement is provided which makes such layer 28 desirable.
~ 7
3~ t~.
~A platinum lead 32 is connected to the layer 28 by a current collector ring 34 in similar fashion to the lead 24. A sc)lution of chloroplatinic acid deposited over the layers 18, 28 and the current collectors 20, 22 and 34 provides a lattice of porous platillum particles 38 (Fig. 2) which extends throuyhout the sponge-like pores in the porous layers and pro~ides a myriad of 3-phase catalyst reaction sites. Ttle particles 38 provide improved cond~ctivity across the solid electrolyte surface to the current collector members.
The cell 10' shown in Figure 3 represents a pre~Qrred embodiment of the inv~ntion which is generally identical to the cell 10 oF Figure 1 bu-t differs in that the substrate 12' is recessed in its center at 429 44 so that the porous layers 18', 28' can be flush with the outer rim portion 46.
As previously discussed, the recessing of the substrate lowers its impedance., Figure 5 is a microphotograph taken at 2000X magnification with a scanning electron microscope of a 12 ~ thick porous zirconia layer (such ~ as the layer 18 in Figure 1) on a ~irconia substra~e. I~ is clearly evi-- dent that two ranges of porosity are distributed in the sintered porous zirconia (white areas) coating: a large macropore structure (black areas) of approximately 1-10~ in diameter and a microporous network of approximately 0.01 to 0.1 ~ in pore diameter which is continuous be~ween the fine particles of the sintering network. These macro- and microporous networks are nat-ural1y developed in the sintering process of loosely compacted fine powders.
Artificia1 macropore and super-macropore distributions, the la-tter ranging from 1 ~ to 1000~ in diameter, (Fig. 4~ can be designed into fine-particle zirconia matrices 48 by incorporating small rod-like ; elements 50 of organic fibers such as are made with acrylic or nylon resins, loading them into the ceramic paste-body to a degree to `~ assure sufficien~ tangential contact between the fibers, drying to set l -the matrix, and then burning out the fibers leaving the artificial macro-pore structure intact. This permi-ts a graduation in pore sizes oF dif~u-sion regions to be incorporated in-to the extended solid electrolyte matrix so that deeper layers within the matrix are in nearer dif~usion-equilibrium with the reactant equilibrium gas. A Final (Fighre 8)extension of arti-ficial macropore construction applies to fuel ce11s, and would permit con-struction o~ an array of continuous linear pipes 54 in the pore bed 56, lying parallel ~a and on bo~h sides o~ the dense electrolyte surface S8.
The pipes or tubes may have a diameter o~ from .040-0.500 inches with a length to diameter ratio of ~en or more. With one end of the pipe array plugged as shown a~ 60~ en~rant fuel or oxidant gas may be pumped into either side of the solid reactor surface-bed 56; allowing high ~emperature fuel cell reactors to be constructed with higher current capacity than could be obtained under the limiting restriction oF a gas difFusional pro-cess. The solid oxygen ion conducting electrolyte 58 in the fuel cellembodiment shown can be stabilized ~irconia or one of seYer~l other suitable materials such as cerium oxide.
In order that the present inven~ion may be more completely under-stood, the following examples are given to describe the method of making a low impedance cell and to demonstrate the dual function of the extended surface o~ this construction: the cell functions firstly as a high sur~ -face area catalyst support, wh;ch when actl~ated, serves in the mode dis-closed in~Pa~ent 3,935,089 to bring the incompletely reacted sampled gases to thermodynamic equilibrium by offering energetic surface sites which promote equilibration reactions; secondly, as a "fanned-out" extension of the 0= conducting solid electrolyte matrix, it minimizes cell polarizations caused by accretion of gaseous reaction products generated by the cell opera~ion. In this latter polarization-1imiting mode, i~ will be shown that the operationally-generated occluding gas Films are diffusion-. I .
g , limited in their removal, and that improved cell per~ormance in the form oFlower impedance and higher 0~ transport capability, can be obtained with the extended surface solid electrolyte system at hi~her rates oF sampled gas transport across the face oF the sensor.
EXAMPLE I
A planar-surfaced dense 8-1/2 mole % ~203-ZrO2 disc 12 shown incorpora~ed in the sensor housing of Figure 1 was coated on both sides with circular patterns of fine 8-lJ2 mole % Y203-ZrO2 powder suspended as a pigment in a thiok film ink. The dried ink pattern 18 was approxi-mately 1/4" dia x .005" thick. After air drying, firing at 1500 00 for 1 hour sintered the powder into ionic continuity with the dense discj still retainin~ the porosity shown on the SEM photomicrograph o~ Figure 5. A
current-collec~or ring 20 of platinum ink (Figure 2) was drawn around the periphery of the 0025" dia film coating 18, and fine lines 22 crossed the fired pad in a spoke-and~wheel configuration. Firing of the current collector was achieved at 950 C. in an air oven.
The disc was then glass-sealed by a glass frit 13 in~o the recessed end of a forsterite ceramic tube 16 to provide isolation of the sensing and reference electrode faces. Platinum~paste jumper intercon-nections 32', 24' were fired over the s~aling-ring 20 to connect the cur-rent collectors 20, 22 on the disc surfaces to prepare platinum conductor stripes 32, 24 axially-located on the inner and outer surfaces of the forsterite tube. The sensor faces were then catalytically activated by applying 5 mg Pt as chloroplatinic acid solution to each porous yttria-zirconia sintered film, and hydrogen firing for 30 minutes at 225 C. The tube was then moun~ed in a metal housing for insertion into a bench test apparatus which passed preheated mixtures of C0 and air to generate equivalent A/F ratios.
: - 10-`
., Results Figure 6 shows the output o-F the sensor fabricated as per Example I as a function of A/F ratio. Not only is the Nerstian transition abrupt at sto~chiometry (S) as reportecl by U.S. Patent 3,935~089~ where:
E = 4RTF ln ~ ~ea~ and where R is the gas constant~ T is the absolute temperature, F is the Faraday constant, P02 is the partial pressure o-f oxygen in ihe reference and gas atmospheres respec~ively, b~ th2 cell output at low A/F ratios shows the inversion oF temperature dependenc~ not predicted by the Nerstian relationship above. Eddy (IEE Transactions an ~ehicular Technology, Vol. VT-23, No. 4, NOVD ~ 1974) has shown that this in verted temperature relationship is due tn the increasing dissociation of C0 at higher temperatures, giving C02 ~ C0 ~ 1/2 2~
The excess 2 liberated produces a leaner (lower output3 signal than might othe~ise be obtained. Eddy describes this ~nverted temperature relationship as due to ideal catalytic activity in bringing the exhaust gas to thermodynamic e~uilibrium at the sensing electrode. This result has b~en achieved without the use of alumina in the catalyst-suppQrt system as pre-scribed by~Patent 3~35,U89 and shows the dual function of the extended surface coating, in that the measured gas sample may be brought to cataly~ed equilibrium, giving not only the sharp Nerstian step function a~ stoich1nm , etry, but also providing the appr~priate inverted thermal response charac j teristic at low A/F ratios.
, .
EXAMPLE II
A second cell was prepared as in Example T except that 6.25 mg o~
P~ were deposited on each electrode in the cataly-tic activation step~ The cell was mounted in the test apparatus described above and cell output was measured at various temperatures and sample gas transport rates as a function . .
. ~
of the resistive load across the cell. The ce'll impeclance was indirectly measured as eciual to the adjus~ed resistive load which lowered the cell terminal voltage to one-half the open circuit potential.
Results The data of Figure 7 cletail the test results of two cells. ~he cells comprise an extended-sur~ace Y203-ZrO2 cel'l as silown in Fig. I and a planar Y203-ZrO2 prior art type cell fabricated as shown in Figure 1 but without the sintered Y203-~rO2 extended sur~ace. From the data the following conclusions can be drawn:
1) In comparing curves A and C, the extended surface ~irconia cell has a lower impedance than the plane-surfaced cell (approximately lO,OO~fi~ersus ~60,aoo v~) when operated at 540 C.
2) At 650 C. (compare curves E and F~ the extended surface cell has an impedance in the range oF 750 ~ 15~d~while khe planar surface zirconia cell has an impedance in the 70 ~ 20 kl~range.
3) Increasing gas flow rate (compare A versus B, ~ versus ~) over the same sensor showed a decrease in RI f~J 50% For the planar ZrO2 sensor and an approximate 2/3 decrease in RI For the extended surface Zr2 sensor. This indicates that at these flow ra~es the nature o~ the 2Q polarization developed on discharge during cell measurement in an accumu-lation of oxidized by-product at the sensing inter~ace and possibly reduced by-product (nitrogen enriched air) at the reference interface, and that higher gas velocities aid in the removal of these collected impuritiesO
It is also apparent that when comparing the two types of sensors, the cell with exkended surface ZrO2 interfaces will allow more o~ this by-product to collect on its larger surfaces before developing surface polarizations which add to RI, its internal resiskance.
~ ~6~
In overall conclusion, it has been shown that an enhance~-surface stabilized zirconia solid electrolyte can perForm the dual function of:
(l) a catalyst support, which when platinum activatecl3 promotes the attainW
ment af thermodynamic equilibrium in partially reacted gas mixtures at the outermost regions of the particulate matrix From the dense electro-lyte body, and (2) an increased surface providing a greater number of sites ~or O= ion transduction across the solid gas interfaces~ On the sensing electrode surFace~ considering the res;s~ance oF the longer ionic conduc-tion paths within the extended particulate matrix~ it would appear -that this latter function is served in the innermost regions o~ the particula~e : matrix adjacent to the dense electrolyte body, interacting the transduced oxygen with the downwardly-diFfusing thermodynamically equilibrated sensed gas.
\
, ' . .
:, ~ - - 13 -
~A platinum lead 32 is connected to the layer 28 by a current collector ring 34 in similar fashion to the lead 24. A sc)lution of chloroplatinic acid deposited over the layers 18, 28 and the current collectors 20, 22 and 34 provides a lattice of porous platillum particles 38 (Fig. 2) which extends throuyhout the sponge-like pores in the porous layers and pro~ides a myriad of 3-phase catalyst reaction sites. Ttle particles 38 provide improved cond~ctivity across the solid electrolyte surface to the current collector members.
The cell 10' shown in Figure 3 represents a pre~Qrred embodiment of the inv~ntion which is generally identical to the cell 10 oF Figure 1 bu-t differs in that the substrate 12' is recessed in its center at 429 44 so that the porous layers 18', 28' can be flush with the outer rim portion 46.
As previously discussed, the recessing of the substrate lowers its impedance., Figure 5 is a microphotograph taken at 2000X magnification with a scanning electron microscope of a 12 ~ thick porous zirconia layer (such ~ as the layer 18 in Figure 1) on a ~irconia substra~e. I~ is clearly evi-- dent that two ranges of porosity are distributed in the sintered porous zirconia (white areas) coating: a large macropore structure (black areas) of approximately 1-10~ in diameter and a microporous network of approximately 0.01 to 0.1 ~ in pore diameter which is continuous be~ween the fine particles of the sintering network. These macro- and microporous networks are nat-ural1y developed in the sintering process of loosely compacted fine powders.
Artificia1 macropore and super-macropore distributions, the la-tter ranging from 1 ~ to 1000~ in diameter, (Fig. 4~ can be designed into fine-particle zirconia matrices 48 by incorporating small rod-like ; elements 50 of organic fibers such as are made with acrylic or nylon resins, loading them into the ceramic paste-body to a degree to `~ assure sufficien~ tangential contact between the fibers, drying to set l -the matrix, and then burning out the fibers leaving the artificial macro-pore structure intact. This permi-ts a graduation in pore sizes oF dif~u-sion regions to be incorporated in-to the extended solid electrolyte matrix so that deeper layers within the matrix are in nearer dif~usion-equilibrium with the reactant equilibrium gas. A Final (Fighre 8)extension of arti-ficial macropore construction applies to fuel ce11s, and would permit con-struction o~ an array of continuous linear pipes 54 in the pore bed 56, lying parallel ~a and on bo~h sides o~ the dense electrolyte surface S8.
The pipes or tubes may have a diameter o~ from .040-0.500 inches with a length to diameter ratio of ~en or more. With one end of the pipe array plugged as shown a~ 60~ en~rant fuel or oxidant gas may be pumped into either side of the solid reactor surface-bed 56; allowing high ~emperature fuel cell reactors to be constructed with higher current capacity than could be obtained under the limiting restriction oF a gas difFusional pro-cess. The solid oxygen ion conducting electrolyte 58 in the fuel cellembodiment shown can be stabilized ~irconia or one of seYer~l other suitable materials such as cerium oxide.
In order that the present inven~ion may be more completely under-stood, the following examples are given to describe the method of making a low impedance cell and to demonstrate the dual function of the extended surface o~ this construction: the cell functions firstly as a high sur~ -face area catalyst support, wh;ch when actl~ated, serves in the mode dis-closed in~Pa~ent 3,935,089 to bring the incompletely reacted sampled gases to thermodynamic equilibrium by offering energetic surface sites which promote equilibration reactions; secondly, as a "fanned-out" extension of the 0= conducting solid electrolyte matrix, it minimizes cell polarizations caused by accretion of gaseous reaction products generated by the cell opera~ion. In this latter polarization-1imiting mode, i~ will be shown that the operationally-generated occluding gas Films are diffusion-. I .
g , limited in their removal, and that improved cell per~ormance in the form oFlower impedance and higher 0~ transport capability, can be obtained with the extended surface solid electrolyte system at hi~her rates oF sampled gas transport across the face oF the sensor.
EXAMPLE I
A planar-surfaced dense 8-1/2 mole % ~203-ZrO2 disc 12 shown incorpora~ed in the sensor housing of Figure 1 was coated on both sides with circular patterns of fine 8-lJ2 mole % Y203-ZrO2 powder suspended as a pigment in a thiok film ink. The dried ink pattern 18 was approxi-mately 1/4" dia x .005" thick. After air drying, firing at 1500 00 for 1 hour sintered the powder into ionic continuity with the dense discj still retainin~ the porosity shown on the SEM photomicrograph o~ Figure 5. A
current-collec~or ring 20 of platinum ink (Figure 2) was drawn around the periphery of the 0025" dia film coating 18, and fine lines 22 crossed the fired pad in a spoke-and~wheel configuration. Firing of the current collector was achieved at 950 C. in an air oven.
The disc was then glass-sealed by a glass frit 13 in~o the recessed end of a forsterite ceramic tube 16 to provide isolation of the sensing and reference electrode faces. Platinum~paste jumper intercon-nections 32', 24' were fired over the s~aling-ring 20 to connect the cur-rent collectors 20, 22 on the disc surfaces to prepare platinum conductor stripes 32, 24 axially-located on the inner and outer surfaces of the forsterite tube. The sensor faces were then catalytically activated by applying 5 mg Pt as chloroplatinic acid solution to each porous yttria-zirconia sintered film, and hydrogen firing for 30 minutes at 225 C. The tube was then moun~ed in a metal housing for insertion into a bench test apparatus which passed preheated mixtures of C0 and air to generate equivalent A/F ratios.
: - 10-`
., Results Figure 6 shows the output o-F the sensor fabricated as per Example I as a function of A/F ratio. Not only is the Nerstian transition abrupt at sto~chiometry (S) as reportecl by U.S. Patent 3,935~089~ where:
E = 4RTF ln ~ ~ea~ and where R is the gas constant~ T is the absolute temperature, F is the Faraday constant, P02 is the partial pressure o-f oxygen in ihe reference and gas atmospheres respec~ively, b~ th2 cell output at low A/F ratios shows the inversion oF temperature dependenc~ not predicted by the Nerstian relationship above. Eddy (IEE Transactions an ~ehicular Technology, Vol. VT-23, No. 4, NOVD ~ 1974) has shown that this in verted temperature relationship is due tn the increasing dissociation of C0 at higher temperatures, giving C02 ~ C0 ~ 1/2 2~
The excess 2 liberated produces a leaner (lower output3 signal than might othe~ise be obtained. Eddy describes this ~nverted temperature relationship as due to ideal catalytic activity in bringing the exhaust gas to thermodynamic e~uilibrium at the sensing electrode. This result has b~en achieved without the use of alumina in the catalyst-suppQrt system as pre-scribed by~Patent 3~35,U89 and shows the dual function of the extended surface coating, in that the measured gas sample may be brought to cataly~ed equilibrium, giving not only the sharp Nerstian step function a~ stoich1nm , etry, but also providing the appr~priate inverted thermal response charac j teristic at low A/F ratios.
, .
EXAMPLE II
A second cell was prepared as in Example T except that 6.25 mg o~
P~ were deposited on each electrode in the cataly-tic activation step~ The cell was mounted in the test apparatus described above and cell output was measured at various temperatures and sample gas transport rates as a function . .
. ~
of the resistive load across the cell. The ce'll impeclance was indirectly measured as eciual to the adjus~ed resistive load which lowered the cell terminal voltage to one-half the open circuit potential.
Results The data of Figure 7 cletail the test results of two cells. ~he cells comprise an extended-sur~ace Y203-ZrO2 cel'l as silown in Fig. I and a planar Y203-ZrO2 prior art type cell fabricated as shown in Figure 1 but without the sintered Y203-~rO2 extended sur~ace. From the data the following conclusions can be drawn:
1) In comparing curves A and C, the extended surface ~irconia cell has a lower impedance than the plane-surfaced cell (approximately lO,OO~fi~ersus ~60,aoo v~) when operated at 540 C.
2) At 650 C. (compare curves E and F~ the extended surface cell has an impedance in the range oF 750 ~ 15~d~while khe planar surface zirconia cell has an impedance in the 70 ~ 20 kl~range.
3) Increasing gas flow rate (compare A versus B, ~ versus ~) over the same sensor showed a decrease in RI f~J 50% For the planar ZrO2 sensor and an approximate 2/3 decrease in RI For the extended surface Zr2 sensor. This indicates that at these flow ra~es the nature o~ the 2Q polarization developed on discharge during cell measurement in an accumu-lation of oxidized by-product at the sensing inter~ace and possibly reduced by-product (nitrogen enriched air) at the reference interface, and that higher gas velocities aid in the removal of these collected impuritiesO
It is also apparent that when comparing the two types of sensors, the cell with exkended surface ZrO2 interfaces will allow more o~ this by-product to collect on its larger surfaces before developing surface polarizations which add to RI, its internal resiskance.
~ ~6~
In overall conclusion, it has been shown that an enhance~-surface stabilized zirconia solid electrolyte can perForm the dual function of:
(l) a catalyst support, which when platinum activatecl3 promotes the attainW
ment af thermodynamic equilibrium in partially reacted gas mixtures at the outermost regions of the particulate matrix From the dense electro-lyte body, and (2) an increased surface providing a greater number of sites ~or O= ion transduction across the solid gas interfaces~ On the sensing electrode surFace~ considering the res;s~ance oF the longer ionic conduc-tion paths within the extended particulate matrix~ it would appear -that this latter function is served in the innermost regions o~ the particula~e : matrix adjacent to the dense electrolyte body, interacting the transduced oxygen with the downwardly-diFfusing thermodynamically equilibrated sensed gas.
\
, ' . .
:, ~ - - 13 -
Claims (25)
1. An electrochemical cell comprising a dense, non-porous self-supporting solid oxygen ion-conducting electrolyte member, a porous layer of less dense solid oxygen ion-conducting electrolyte in intimate contact with at least one surface of said member, and a porous catalytic electrode on at least portions of said porous layer, said porous layer having a surface area exposed to said electrode which exceeds the surface area of the dense electrolyte member which it overlies by a factor of at least 50.
2. The electrochemical cell of Claim 1 wherein said porous layer has a surface area exposed to said electrode which exceeds the surface area of the dense electrolyte member which it overlies by a factor of at least 100.
3. The electrochemical cell of Claim 1 wherein said non-porous electrolyte member comprises stabilized zirconia.
4. The electrochemical cell of Claim 1 wherein said non-porous electrolyte member comprises cerium oxide.
5. The electrochemical cell of Claim 1 wherein said dense elec-trolyte member includes a central portion of reduced thickness, said porous layer of less dense electrolyte overlying said central portion.
6. The electrochemical cell of Claim 1 wherein a metal current collector overlies spaced apart portions of the porous layer and said porous catalytic electrode overlies and is in electrical contact with said current collector.
7. The electrochemical cell of Claim 6 wherein said dense electrolyte member is in the form of a water.
8. The electrochemical cell of Claim 7 wherein said current collector overlies the porous layer in a pattern similar to a spoked wheel.
9. The electrochemical cell of Claim 6 wherein said porous catalytic electrode comprises platinum.
10. The electrochemical cell of Claim 3 wherein said zirconia is stabilized with yttria.
11. A method of lowering the output impedance of an electro-chemical cell having a dense substrate of an ion-conducting solid electro-lyte material of a predetermined thickness: comprising the steps of coating at least a portion of one surface of the substrate with a coating of very fine particles of a porous ion-conducting solid electrolyte of the same chemical composition as said dense substrate; applying current collectors to each side of said substrate; and applying a catalyst con-taining solution to at least portions of said coating to catalytically activate said coating, said current collectors and catalytically acti-vated coating being in electrically conducting relationship and the sur-face area of said coating being at least 50 times greater than the surface area of the substrate to which it is applied.
12. The method of Claim 11 wherein said solid ion-conducting electrolyte is adapted to be exposed on one surface to a gas to be sensed and on another surface to a reference gas, said method including the additional step of applying said coating to both said sensing gas surface and said reference gas surface.
13. The method of Claim 11 wherein said solid ion-conducting electrolyte is adapted to be exposed on one surface to a gas to be sensed and on another surface to a reference gas, said coating of fine particles being applied to at least a portion of the electrolyte surface which is adapted to be exposed to a gas to be sensed.
14. The method of Claim 13 wherein said substrate has a central portion of its surface area removed to reduce its center thickness before said coating is applied.
15. The method of Claim 11 wherein said coating is fired and sintered before said electrodes and catalyst containing solution are applied.
16. The method of Claim 15 wherein said catalyst containing solution is chloroplatinic acid.
17. An oxygen sensor for sensing the difference in oxygen con-tent between an exhaust gas from a combustion process and a reference gas, said sensor including a body member and an oxygen ion-conductive member of dense non-porous stabilized zirconia sealed in said body so one side is exposed to said exhaust gas and the other to said reference gas, one end of said zirconia member being coated on at least a portion of the surface thereof which is adapted to be exposed to an exhaust gas with a porous thick film coating of stabilized zirconia, a porous catalytic electrode in contact with the exposed surface of said coating, and current collectors in contact with the opposite sides of said zirconia member, said porous thick film coating having a surface area exposed to said electrode which exceeds the surface area of the dense zirconia member which it overlies by a factor of at least 50.
18. The oxygen sensor of Claim 17 wherein said body member is of tubular, non-ion-conducting ceramic and said oxygen ion-conductive member is in the shape of a disc, said disc being hermetically sealed in one end of said tubular ceramic body member.
19. The oxygen sensor of Claim 18 wherein said current collec-tor which is in contact with the exhaust gas side of said zirconia member overlies said porous catalytic electrode and is arranged in a spoke-like pattern.
20. The oxygen sensor of Claim 18 wherein said zirconia member is stabilized with yttria and said porous electrode and current collectors are platinum.
21. The electrochemical cell of Claim 1 wherein said porous layer of electrolyte has a pore structure in which at least some of the pores have a diameter in the range of 1-10µ.
22. The electrochemical cell of Claim 1 wherein said porous layer of electrolyte has a pore structure in which at least some of the pores have a diameter in the range of .01-.1µ.
23. The electrochemical cell of Claim 1 wherein said porous layer of electrolyte has a pore structure in which at least some of the pores have a diameter in the range of .01-10µ.
24. The electrochemical cell of Claim 1 wherein said porous layer of electrolyte has a pore structure in which at least some of the pores having a diameter in the range of 10-1000µ.
25. The electrochemical cell of Claim 1 wherein said porous layer of electrolyte has tubular passages formed therein which have at least one end open externally of said cell for permitting gas to be pumped into said porous layer, said tubular passages having a diameter in the range of .040-.500 inches.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US75092276A | 1976-12-15 | 1976-12-15 | |
| US750,922 | 1976-12-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1096441A true CA1096441A (en) | 1981-02-24 |
Family
ID=25019684
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA293,041A Expired CA1096441A (en) | 1976-12-15 | 1977-12-14 | Electrochemical cell having enhanced-surface non- conducting solid electrolyte and method of making same |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS53101485A (en) |
| CA (1) | CA1096441A (en) |
| DE (2) | DE2755650A1 (en) |
| ES (2) | ES465653A1 (en) |
| FR (1) | FR2374640A1 (en) |
| GB (1) | GB1591898A (en) |
| IT (1) | IT1089129B (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1121360B (en) * | 1978-06-12 | 1986-04-02 | Broken Hill Pty Co Ltd | REFINEMENTS WITH GAS SENSORS |
| CA1119250A (en) * | 1978-09-13 | 1982-03-02 | Bendix Autolite Corporation | Process for producing an activated oxygen gas sensor element |
| CA1125857A (en) * | 1978-09-13 | 1982-06-15 | Ching T. Young | Process for producing a solid electrolyte oxygen gas sensing element |
| US4225559A (en) * | 1979-01-22 | 1980-09-30 | Ford Motor Company | Ceramic element sensor |
| JPS55152451A (en) * | 1979-05-18 | 1980-11-27 | Toyota Motor Corp | Oxygen sensor with solid electrode |
| FR2488408A1 (en) * | 1980-08-08 | 1982-02-12 | Carbonisation Entr Ceram | Oxygen determn. appts. esp. for exhaust gas from motor vehicles - using thin solid electrolyte coated on each side with thin metal film electrode to make probe which can be rapidly heated |
| US4477541A (en) * | 1982-12-22 | 1984-10-16 | The United States Of America As Represented By The United States Department Of Energy | Solid electrolyte structure |
| JP2502961B2 (en) * | 1984-04-26 | 1996-05-29 | 日本碍子株式会社 | Method for manufacturing electrochemical device |
| JPS6118857A (en) * | 1984-07-06 | 1986-01-27 | Ngk Insulators Ltd | Manufacture of electrochemical cell |
| JPH0623718B2 (en) * | 1986-03-18 | 1994-03-30 | 科学技術庁無機材質研究所長 | Oxygen ion conductivity measurement device |
| ES2017658B3 (en) * | 1986-04-17 | 1991-03-01 | Pierre Beuret | PROBE TO MEASURE THE PARTIAL OXYGEN PRESSURES IN A GAS ATMOSPHERE WITH RESPECT TO A REFERENTIAL ATMOSPHERE |
| JPH0752171B2 (en) * | 1987-05-30 | 1995-06-05 | 日本碍子株式会社 | Electrochemical device |
| DE19541619A1 (en) * | 1995-11-08 | 1997-05-15 | Bosch Gmbh Robert | Electrochemical sensor and method for producing an electrochemical sensor |
| GB0316504D0 (en) | 2003-07-15 | 2003-08-20 | Rolls Royce Plc | A solid oxide fuel cell |
| JP7003748B2 (en) * | 2018-03-09 | 2022-02-10 | 富士電機株式会社 | Zirconia Oxygen Sensor Parts and Zirconia Oxygen Sensor |
-
1977
- 1977-12-14 IT IT30703/77A patent/IT1089129B/en active
- 1977-12-14 DE DE19772755650 patent/DE2755650A1/en not_active Withdrawn
- 1977-12-14 GB GB51960/77A patent/GB1591898A/en not_active Expired
- 1977-12-14 DE DE19777738098U patent/DE7738098U1/en not_active Expired
- 1977-12-14 CA CA293,041A patent/CA1096441A/en not_active Expired
- 1977-12-15 FR FR7737891A patent/FR2374640A1/en active Granted
- 1977-12-15 JP JP15115377A patent/JPS53101485A/en active Pending
- 1977-12-31 ES ES465653A patent/ES465653A1/en not_active Expired
-
1980
- 1980-01-16 ES ES487745A patent/ES487745A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1591898A (en) | 1981-07-01 |
| FR2374640B1 (en) | 1981-10-02 |
| ES465653A1 (en) | 1980-07-01 |
| ES487745A1 (en) | 1980-09-16 |
| DE2755650A1 (en) | 1978-06-22 |
| DE7738098U1 (en) | 1978-11-09 |
| FR2374640A1 (en) | 1978-07-13 |
| JPS53101485A (en) | 1978-09-04 |
| IT1089129B (en) | 1985-06-18 |
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