CA2085355A1 - Metal and metal oxide catalyzed electrodes for electrochemical cells, and methods of making same - Google Patents
Metal and metal oxide catalyzed electrodes for electrochemical cells, and methods of making sameInfo
- Publication number
- CA2085355A1 CA2085355A1 CA002085355A CA2085355A CA2085355A1 CA 2085355 A1 CA2085355 A1 CA 2085355A1 CA 002085355 A CA002085355 A CA 002085355A CA 2085355 A CA2085355 A CA 2085355A CA 2085355 A1 CA2085355 A1 CA 2085355A1
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- Prior art keywords
- porous
- catalytically active
- electrode
- active layer
- electrodes
- Prior art date
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/52—Removing gases inside the secondary cell, e.g. by absorption
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
-
- 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
- Y02E60/10—Energy storage using batteries
-
- 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
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Inert Electrodes (AREA)
Abstract
Porous electrodes for use in fuel cells and other electrochemical cells comprise a non-noble metal catalytically active layer on a porous conductive substrate. The loading of the catalytically active layer is lower in terms of weight of catalyst per unit area of geometrical electrode surface than heretofore. Several alternative methods of forming the electrodes impregnating a porous conductive substrate with a metal salt solution, followed by chemical or thermal formation of the porous catalytically active layer;
mixing the catalytically active material of the porous conductive substrate, followed by fabrication of the electrode; or depositing pyrolitic carbon from the gas phase onto a porous conductive substrate, at elevated temperatures in a gas atmosphere. The electrode may have a porous metallic current collector, and a further gas diffusion layer. The electrodes of this invention have particular utility in alkaline primary or secondary cells as auxiliary gas recombining electrodes, especially as oxygen consuming auxiliary transfer electrodes.
mixing the catalytically active material of the porous conductive substrate, followed by fabrication of the electrode; or depositing pyrolitic carbon from the gas phase onto a porous conductive substrate, at elevated temperatures in a gas atmosphere. The electrode may have a porous metallic current collector, and a further gas diffusion layer. The electrodes of this invention have particular utility in alkaline primary or secondary cells as auxiliary gas recombining electrodes, especially as oxygen consuming auxiliary transfer electrodes.
Description
- WO`91/20102 . 2 0 8 ~ 3 S ~ PCI/CA91/00192 II~ETAL AND I~ET~L OXIDE CAT~LYZED ELECTRODES
FOR l~:LECTROC~EI~ I CAL CELLS, ~ND UETEIODS
OF ~AK I NG S~E
FI15LD OY THE INVENTION:
This invention relates to porou~ electrodes for fuel cells and similar cells such as air-metal cells, and alkaline zinc/manganese dioxide cells (particularly secondary cells), or other primary or secondary alkaline cells, and to the methods of making the present electrodes. In particular, the invention relates to porous electrodes which may be used a~ fuel cell cathodes or as auxiliary gas recombininy or transfer electrodes in alkaline cells, wherein a catalytically active layer i~
formed on a porous conductive substrate, and the catalytically active layer is derived from non-noble ~etals. In the event that the porous electrode is to be used as a fuel cell anode, a further small amount of a .. ,; ~.
noble metal is included in the catalytically active layer. ~.
In all events, electrodes according to the present invention have a lower loading of catalytically active .. ..,, ~, . . . . .
layer in terms of weight of catalyst per unit area of geometric electrode surface than heretofore, but with r r; ,~. , .
operating characteristics that compare favourably with prior art electrodes having noble metal catalysts, but being available at much reduced cost~.
., .. '' . ', ' ' ' . . ' " ~ ~ , ' . ', "' . , ~ , ,' ' ' ' ' ' ' .. , ' ' .. , ' ' ' ' ,.
.' ' ' ' ', . ' ', ~, . '. ' ' ' , . ' ,, ' , , , ", ~ .' ' ' , . . ' " ' , ' Wo91/20tO2 ` ' ~ ~8 ~ 3 ~ ~ PCT/CA91/OOt92 ~
. ., The present invention teaches several alternative methots for producing electrodes according to the present invention; whereby the electrode, once produced, will in all events have a catalytically active layer on a porous conductive substrate. Electrodes of the present invention may comprise a porous metal current collector, and a further gas diffusion layer, with the current collector being situated or embedded in the porous conductive ~ubstrate or within the gas diffusion layer.
J~CRGROIJND O~ T~l~ INVl~NTION:
The prior art has concerned itself, for many years, with the provision of porous electrodes that are particularly intended for use in fuel cells. However, while many ~uite acceptable electrodes have bcen provided in the prior art, it has been the general e~perience that ~uch electrodes are expensive to produce. This comes, especially, due to the generally accepted reguirement ~or the u~e of noble metals in fuel cell electrodes, including . ~ , .
especially gas diffu~ion or poro~s electrodes. Moreover, ; whén the prior art has provided electrodes ~hich comprise - , . - . - , . . .
a porous substrate having a porous catalytically active -, . . : ~ . . , layer theroon, it has been common in the past for there to be relatively high catalyst loading by weight per unit ,, . . :. ,. : ., , . .. . , . . i ar~a of ~eometrical electrode sur~ace, thereby contributing further to the cost of ~roducing such ' ' , ~ ` ', ~ ' ' ' . . ', ~ ' i ' ` .
WOsl/20102 ~ PCTtCA91/OOt92 20853~
electrodes.
Such prior art has included KORDESCH et al United States Patent 3,405,010 dated October 8, 1968, and XORDESCH United States Patent 3,310,434, dated March 21, 1967. The former patent relates to the catalyzing of porous electrodes, using a heavy metal salt, an aluminum salt, and a ruthenium salt. The latter patent is particularly related to the use of noble metals as catalysts on a porous electrode.
Yet another KORDESCH patent relating to the use of wet proofed conductive substrates having an active conductive layer with a surf?ce-deposited noble metal catalyst is United States Pa~cnt 3,899,354 issued August 12, 1975.
BARER et al in United States Patent 3,935,029 issued January 27, 1976 teach the use of fine graphite particles enmeshed in a web of polytetrafluoroethylene (PTFE), however, once again using noble metals.
Thus, it is a principal purpose of the present invention to provide catalyzed electrodes having excellent performance charac~eristics, at low cost. The catalyzed electrodes of the present-.invention are~-specifically ~dapted for use in fuel cells and metal-air cells; and especially u~eful as auxiliary gas recombining electrodes in alkaline zinc/manganese dioxide cells (particularly secondary cells), or-other primary or secondary alkaline -..
" . ~ '.' .~ ' ' ' ' ' ` ' . " ~ , 2 08 ~:3`~
cells. The porous catalyzed electrodes of the present invention have particular utility as oxygen reduction electrodes in alkaline cells as noted above.
Thus, the present invention comprises the provision of a porous electrode which comprises a porous conductive ~ubstrate and a porous catalytically active layer on the porous conductive substrate; the porous conductive substrate being chosen from the group consisting of carbon, graphite, and metal: and the porous catalytically active layer being chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, carbon, carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal. (If used as an anode in a fuel cell, the electrode of the present invention is as described above, together with a further additional smaller amount of a catalytically active noble metal or carbon together with a catalytically active noble metal.)-Catalytically active non-noble metals that are particularly ¢ontemplated for use in the present invention include iron, cobalt, nickel, manga~ese, chromium,-coppor, and vanadium: and catalytically active noble~metals there parki¢ularly.intended for~use in the present invention, in anodes according to this invention, include platinum, ~allædium, rhodium, iridium, osmium, gold, silver, and WO91/20102 2 0 8 5 ~ 5`: ~ PCT/CA91/00192 ruthenium.
In general, a porous electrode according to the .
present invention may include the porous active layer cho~en from the group consisting of carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal;
and very often, the porous active layer may further ~.
comprise polytetrafluoroethylene (PTFE3, as a binder. The t~`
carbon may be graphite.
Generally speaking, fuel cells may be considered to :~
be galvanic cells, with the basic reaction being the electrochemlcal oxidat.ion of a fuel and the electrochemical reduction of an oxidant (e.g., oxygen).
It should be noted, however, that fuel cells differ from ordinary primary cell9 ~uch a~ commercially available dry cells, in that tho fuel and o~idant are generally introducod continuously into the cell electrodes during the production of electricity. Thus, theoretically, the eloctrodes and electrolyte of fuel cells qhould maintain a constant value, during the time when the fuel and the o~idant are reacted electrochemically within the fuel cell, and-electricity and the. product of~ reaction --usually water -- ar- removed from the fuel cell.
~ ~ ~here ~has been, for the la t century or-so, a .continuing search for ways to boost the electrical output of fuel cell~, and/or to increa~e their ~ervice life, ~.
.:
, ~ .
Wo91/20102 2 0 8 ~ 3 ~ ~ ; PCT/CA91tO0192 .
and/or to lower the cost of producing fuel cells so as to render them commercially feasible. Needless to say, one major area for research has been the catalysis of reactions which take place within the electrodes of fuel cells, and thereby the requirement for discovering new methods of depositing known catalysts either in a more active form or more economically. However, the search still continues for catalysts which will raise the current density within electrodes, and/or the voltage of the cell, to levels which approach those that are attainable in theory.
On the other hand, .there has also developed a prsssing need for gas recombining electrodes in closed cells such as alkaline zinc/manganese dioxide cells --especially secondary c-lls. In such cells, there may be a periodic (or continuing) generation of gasses, and particularly there may be evolution of gaseous oxygen on charge, overcharge, or any reversal. of cell polarity.
Such cells typically operato over. a broad range of temperatures (e.g. from -40 to ~65 degrees Celsius) and at current densities where the auxiliary porous electrode may itself be reguired to pass up..to 7~0 mA/sg. cm.
It is the position of the present inventors that the present i~vention provides a major step..in:the.required direction, by providing.catalyzed porous condu~tors having relatively low production costs, and with excellent .. . .. .... .. . . ~ . . .. , . . .. . . , . ., .. . ,, .. .... .. . . ... ~ . .. .............. ... . ... . ... ..... .
. ... . .. .... . . .. . ...
wo gt/20l02 2 0 8 5 3 S ~ PcrtcAg1/00l92 . . . .
characteristics as to their efficiency, power density, performance, and life. The characteristics of electrodes according to the present invention compare most favourably with the characteristics of certain higher efficiency prior art fuel cell electrodes which, however, contained noble metals in all instances and which therefore were costly to produce.
When used as a catalyzed porous electrodes in fuel cells or alkaline zinc/manganese dioxide cells, electrodes of the present invention may comprise a porous gas tiffusion layer adhered to the porous conductive substrate spoken of above, at one side thereof. In fuel cells, electrodes according to the present invention may also generally include porous metal current collectors, as a conveniont way of conducting electrical current produced in the fuel cell out of the fuel cell.
In general, the catalyst provided by the present invention is insoluble within the operating voltage and the operating condition range of the electrode, thereby contributing to the life of the electrode. This means that-catalyzed porous electrodes according to the present invention may be used with such electrolytes as alkaline electrolytes,-for example potassium--hydroxide as used in zinc/manganese dioxide cell~s. It also makes the use of cataly~ed porous electrodes according to the present i~vention in mstal-air batteries and cells more . . . ~ . ,; :: , , ~ ~ .
. . . : . .,: . : . i . .
:-WO91/20102 2 ;0 8 5 ~ ~ 5 PCT/CA9t/00192 .- .
8 ;~
attractive. -. The inventors herein have discovered, guite unexpectedly, that the addition of a metal or metal oxide from the group consisting of iron, cobalt, nickel, manganese, chromium, copper, and vanadium -- all non-noble .
metals -- to a porous electrode provides an electrode having a service life and performance characteristics comparable to those of platinum catalyzed electrodes.
Clearly, the cost of electrodes according to the present invention, when compared to the cost of a platinum, catalyzed electrode, may be considerably lower. Moreover, platinum catalyzed electrodes may have significant carbon corrosion o~ the carbon within the porous substrate structure, whereas the use of metals and metal oxides according to the present invention significantly decrea~es the risk of carbon corrosion. That fact contributes, therefore, to the attractiveness of electrodes accordinq to the present invention for u~e in alkaline cell systems, and metal-air batteries. In addition, dissolved trace amounts of noble metals can cause problems in metal-air or other-batteries containing a zinc, iron or aluminum anode .. by.: enhancing the.hydrogen evolution (gassing;reaction).
.. This.enhanced. anode.corrosion cau~es high salf-discharge and can result in cell leakage.
According to the present invention, the porous conductive substrate of electrodes may be carbon, .-;
WO91/20102 2 0:8 3;3:S à PCT/CA91~00192 graphite, or metal; or, indeed, any other suitable conductive material. The porous active layer may comprise a catalytically active non-noble metal as discussed above, an oxide of a catalytically active non-noble metal, carbon, carbon toqether with a catalytically active non-noble metal, and carbon together with a oxide of catalytically active non-noble metal. Typically, the porous active layer consists of carbon together with a catalytically active non-noble metal or carbon together with an oxide of catalytically active non-noble metal; and in either case, it may further comprise a binder, usually PTFE.
A typical porous electrode accordlng to the present invontion would consist of an electrochemically active layer which may be typically from 50 to 500 microns thick, and it may further include a gas diffusion layer which may also be 50 to 500 microns thick. If used in a fuel cell, the clectrode would usually also have a metal scroen current collector (a porous metallic current collector) embedded in an electrode layer -- unless a bipolar 'con~truction method is applied. The electrochemically active~'layer,-as noted,'-would contain the electrocatalyst as described'àbove,'supported on ~ carbon, graphite or 'metal''porous~sub~trate,~"and''is located on the electrolyte side of the electrode.
A gas diffusion layer, when used, may typically .. . .. .. . . . . . .. .. . . . . .. . . . .. ..... ..... . . .... .. . . ........ . .. . ..
WO91/20102 2 0 8`~ 3:~ ~ PCT/CA91/00192 consist of PTFE bonded carbon, and would normally have a higher degree of hydrophobicity than the active layer.
During the manufacturing process of the gas diffusion layer, discussed in greater detail hereafter, a pore builder such as ammoniumbicarbonate, may be used. The current collector, when used, may be embedded in either the gas diffusion layer or the active layer; and when electrodes according to the present invention are used in bipolar cells, no current collector is reguired.
Typically, the total electrode thickness of an electrode comprising an active layer, a gas diffusion layer, and a current collector, may range from ioo to 750 microns.
Thus, porous olectrodes according to the present invention may comprise a porous conductive substrate, and a porous gas diffusion layer adhered to one side thereof.
As notcd, the porous active layer is at a first side of the porous conductive substrate, and the porous gas dif$usion layer is at the ~ide of the porous conductive substrate opposite to that of the active layer. Of course, the porous active layer may permeate the porous conductive substrate, and in any event the porous gas diffusion layer i adhered to one side thereof. ,-~ - ~s noted above, electrodes according to the present - invention may also ~e used as anodes in fuel cells, in which ~ase a further additional smaller amount of a .. .. . . . .. . . . ... . ... . . . ... .
~Q~3~
catalytically active noble metal or carbon together with a catalytically active noble metal is added to the catalytically active layer of the electrode. There is little point in providing oxides of catalytically active noble metals, since the oxide would be promptly reduced to the noble metal per se when exposed to the hydrogen fuel generally used ih a fuel cell.
The noble metals contemplated for use in this aspect of the invention are discussed above.
The concentration of catalyst within the porous catalytically active layer is generally in the range of from O.l to lO mg per sguare centimeter of the gèometrical electrode surface area. Typically, the concentration of catalyst wit~in the porous catalytically active layer is in the range of from l to 5 mg per square centimeter of the geometrical electrode surfac0 area.
In general, cathodes for hydrogen/oxygen fuel cells, according to the preqient invention, may have a service life well in excess of two thousand hours at a current density of lO0 mil1iamperes per siquare centimeter, at a voltage above 0.85 volts--versus RHE (Reversible Hydrogen Electrode). Similar electrodes, using non-noble metal oxide catalysts, can be run at up to 300 mil?iamperes per .. . .... ... .. . . . ..
s~uare centimeter on oxyg~n and air, with potentials of about 0.8 volts and 0.79 volts versus RHE, respectively.
As auxiliary gas recombining electrodes used in alkaline - . : .: , ~ , , ,- .,. : . . . . . .
, ; ~ , ~ ; . - .:
W O 9t/20102 2 0 8 5 3 5 ~ P~r/CA91/00192 `
electrochemical cells such as zinctmanganese dioxide cells having potassium hydroxide electrolytes, the electrodes may be successfully subjected to current densities up to 7~0 m~/sg. cm. at low temperatures.
The present invention provides three generally related but tistinct processes for the production of porous electrodes in keeping herewith. Those three general methods may be characterized a~ follows:
I (a) impregnating a porous conductive substrate structure with a compound containing the chosen material for the porous catalytically active layer; and (b) forming the porous catalytically active layer:
II (a) mixing the chosen material for said porous catalytically active layer with the chosen material for the porous conductive substrate;
and (b) fabricating the electrode:
III (a) depositing pyrolytic carbon from the gas phase -onto a porous conductive substrate structure, at an elevated temperature in a gas atmosphere.
The compound used in step (a) of Process I, above, is - : . .
a metal salt solution of thè chosen catalytically active .. . .
metal. The formation process of step (b) of the Process I
may be the chemical formation of the porous active layer, or the thermal formation of the porous active layer.
.. ~ ... .... , ,.: .. ....... .. . . .... ..
, . . . .. . .. .
W O 91/20102 . P~r/CA91/00192 2~8~3~5 ` "
~he chosen active material that is used in step (a) of the Process II, may further be mixed with carbon and ~ ,7'!' PTFE. , The Process III is carried out at least 600 degrees ' C, and the gas atmosphere may be steam, carbon dioxide, ' "
carbon monoxide, ammonia, nitrogen, argon, or hydrogen. ' ".
~RIEF DESCRIPTION OF THE DRAWINGS:
A typical embodiment of the present invention when used as an auxiliary electrode as an oxygen gas recombining electrode in an alkaline zinc/manganese dioxide cell is shown in the singlo Figure of drawing which accompanies the following di~cusslon.
DETAILE~ DESCRIP~ION OF THE ~REFERRED EMBODIMENTS: j'.
The Figure shows a typical cmbodiment of an alkaline zinc/manganese dioxide cell having an auxiliary porous o~ygen ga~ recombining electrode in koeplng with the ' present invention. The cell comprises a steel can 10 having a :conventional.metal oxide cat~ode 12 which is typically fonmed cylindrically around an anode 14. The cathode`l'2'.may.comprise ~inely.divide&.manganese dio~ide '-' and 'gr~phite,-:and the anode. ~ay~compri~e zinc powder.
Between the cathode and the anode is an .electrolyte ' .
permeable separator 16; When the cathode is manganese~ ~' dio~ide and the anode is zinc, then the electrolyte may be an aqueous 301ution of potassium hydroxide. A boss or a .
.. . . . .... .. . . . .. .. . . . . ..... . .... .. . . . . . .. . ... . .
W O 91/20102 PC~r/CA91/OOt92 2`~`g~)35~ ` , .
.
pip 18 is ~ormed at the base of the can 10, to give the cathode or positive contact for the cell.
The electrolyte permeable separator 16 is typically formed of rayon/polyvinyl alcohol. The anode may have at its upper end an auxiliary porous gas recombining electrode 20, which is arranged so as to be wetted by the electrolyte. At its lower end, the anode may be provided with an insulated disc or basket 22, to preclude anode contact with the cathode pip 18.
A current collector nail 24 projects into the anode 14 through a casing cover 26, with the head 28 of the collector nail 24 being on the outside of tho cover 26 to form the anode contact ~or the cell. The cover 26 seals the can 10 by crimping formed around its edge. An additional anode cover 30 i~ provided to give the anode or negative contact for the cell.
The cathode may be provided with auxiliary cathode material to catalyze the reabsorption of hydrogen as set forth in KORDE5CH and TOMANTSCHGER United States Patent 4,925,747 issued May 15, 1990. The ausiliary eloctrode 20 may have the characteristics set forth in TOMANTSCHGER and --KORDESCH United States Patent 4,900,642 issued February 13,-1990. ~
- There follo~ several examples of various electrode -structures according to the present invention, their ~anufacture, and their operating characteristics, ... ... ~. ~.................. .
,~: . . , . - , ,, , .
.. - . , -WO 91/20102 PCltCA9ltOOt92 2'~ 3 5 a' `' ''"
~XAMPLE I:
Under the general steps of Process I noted above, a graphite felt (for example, a graphite product available commercially as PANEX~ CFP 30-10) was impregnated with manganose nitrate solution and pressed into a layer which comprised a mixture of carbon available commercially as SHAWINIGAN BLACRT~ and PTFE. The carbon/PTFE layer comprised 62.5% carbon, 37.5% PTFE.
The catalyst was thermally formed at 300 degrees C, in air, a~d resulted in an electrode having catalyst loading of 1.5 mg. of manganese per sguare centimeter of - :
geometrical electrode surace area. The following table demonstrates the electrode p¢rf ormance, as a cathode at the oxygen side of an o~ygen/hydrogen fuel cell system having 9 N ~OH electrolyte, at 65 degrees C.
Current Density IR free potential ~mA/s~.cm.~ [mV vq. RHE]
(~he IR free potential is determined using laboratory proc~dures a~d standards, and is measured in millivolts as ... , . . . , ., . . .. , ..... , ........ .. ...... ,, .. ... .. , .. ,, .,~. .... ,., .. ~, .. .. . . . ... . . ... .. .. ....
. . ... . .. . .
W O 91t20102 2 a 8 5 3 ~ ~ PC~r/CA91/00192 :: " . ` I
against a Reversible Hydrogen Electrode reference).
~X~hE II:
Again, using the general Process I, an active layer of nickel FIBREX~ felt was impregnated with manganese nitrate solution, and again pressed into a carbon/PTFE
layer as in Example I. The catalyst was thermally formed at 300 degrees C in air, with a catalyst loading of 7.6 mg. of manganese per square centimeter of geometrical electrode surface area.
The electrode performance in an oxygen/hydrogen fuel cell system, having 6 N ~OH electrode, at 20 degrees C, was as foll GWg: :
Current Density IR free potential ~mA/sq.cm.~ tmV vs. RHE]
150 764 ;
~AMP~
In thi~ case, activated carbon plus an active catalyst waq used, in a multi-layer PTFE bonded carbon electrode. .The gas diffusion layer was a carbon~PTFE
layer as described above in Examples I and II.
The active layer comprised carbon black available commercially as VULCANIM XC 72R which was acti~ated to 30%
weight loss in the ~resence of cobalt-aluminum spinel (5 SUBST~TUT~ SHI~
.. . . . . ..
,.' 1 . '. ' ' . ' . , , . ~,.. .. ~ : ' ' ' ' ' . .. ' . ' ... . . ~ . . ..... , . . .. ~ .. :
~ . .... ... - .... . : - :-. ~ . . ' . , - ~, . .
W O 91/20102 2 b 8 5 3 s ~ PC~r/CA91/00192 mmol cobalt, 10 mmol aluminum per 100 grams of carbon), in the amount of 67~ together with graphite in the amount of 22~, and PTFE in the amount of 11%.
The catalyst loading was 5 mg. of manganese dioxide per square centimeter of geometrical electrode surface area, which may also be expressed as 3.2 mg. of manganese per s~uare ~entimeter of geometrical electrode surface area.
The electrode was operated for 220 hours at 100 milliamperes per square centimeter at 65 degrees C in 12 N
KOH. The oxygen and air operation, both, of thé electrode are set forth in the ~ollowing table:
Current Density IR free potential IR free potential ~mA/sg.cm.~ ~mV vs. RHE~ ~mV vs. RHE~
Oxygen Air .....
The electrode wa~ also operated at 150 milliamperes per square centimeter, over a varying range of tomperatures, with air operation being observed as set .... . .. , . . . . . . ...................... . , . ,. , . ~ . . . . . .
-: .
- . : . - : ,; . ... . . .
. ., ,. ,. , ., . . ::
WO9lt20102 2 0 8 5 3 ~ j PCT/CA91/00192 forth in the following table. . -Temperature IR free potential at 150 mA/cm ., tc~ Air operation ~mV vs. RHE]
6~ 834 737 ~.
Finally, oxygen long term performance in 12 N KOH at 65 degrees C, operating at 100 milliamperes per square centimoter, was determined as follows:
Oxygen long term performanco in 12 N K~H at 65 C and 100 mA/cm.l~1 .
time IR free potential at 100 ma/cm ~hrs] ~mV vs. RHE~
500 893.
1000 . 890 lS00 ` 851 .. ~
-. . . . . - ., -~: ~ :
Under the Process III, VULCANTN XC 72R carbon was activat~d in the presence of 5 mmol of cobalt per 100 ',.
-~ WO91/20102 2 0 8 ~ 3 5 S PCT/CA91/00192 `' .:
grams of carbon in the gas phase, in a carbon dioxide ~as atmosphere, at lO00 degrees C. This resulted in an active layer consisting of carbon activated at lOOO-C in carbon dioxide atmosphere, in the amount of 95.2% containing cobalt oxide; with PTFE in the amount of 4.8%
The catalyst loading was determined to be l.3 mg. of cobalt per square centimeter of geometrical electrode sur$ace area.
The electrode performance was determiner in 9 N XOH, at 20 degrees C with oxygen, as follows:
Current Density IR free potential ~mA/sq.cm.] tmV vs. R~E~
0 gO5 l 832 lO0 755 lS0 725 E:Xl~MPLE V:
Along the general lines of preparation of an electrode in keeping with Example II, an anode was fabricated, as follows:
The gas dlffusion layer comprised carbon (SHAWINIGAN
BLACK) in the-amount of 50%, with 50% PTFE.
The actiYe layer comprised superconductive carbon bla~ available commercially as BLACK PEAR~S~ activated , . . , , . .~; . : , WO 91/20102 ~ 2 0 8 ~ 3 5 ~ PCT/CA91/00192 " .
to 30% weight loss in the presence of cobalt-aluminum spinel (5 mmol cobalt, 10 mmol aluminum per 100 grams of carbon), together with ruthenium (0.2 grams Ru per 100 grams of carbon) all in the amount of 80~; with 20% PTFE.
The following table demonstrates the performance of this electrode, as an anode, after 165 hours at 100 milliamperes per square centimeter at 65 degrees C in 12 N :-XOH, with hydrogen:
Current Density IR free potential tmA/sq.cm.] tmV vs. RHE]
O
150 15 `.
Opcration at 150 milliamperes per sguare centimeter over a range of temperatures, resulted in the following: :
:
Temperature IR free potential at 150 :
mA/cm ~C] tmV vs. RXE]
23 .
. 23 ' ~ 565 . - . 26 ~5 36 i:~
; - 40 ` 43 .
;
.- . ....... , - - - . . . . :
W091/20102 2 0 8 ~3S 5 PCT/CA91/OOt92 . ~
Finally, hydrogen long term performance in 12 N KOH ";-at 65 degrees C and lOO milliamperes per square centimeter was determined, with the following results:
timeIR free potential at lOO mA/cm ~hrs] ~mV vs. RHE3 10 .j lOO 39 500 ~S
lOOO 49 lSOO 83 2000 lO9 There have been described 0lectrodes that are ~ntended ~or use as cathodes in fuel cells (or metal-air cells), or as auxiliary gas recombining electrodes in sealed alkaline cells, which electrodes have excellent operatiny characteristics and which are produced without the requirement for use of noble metals. When a small additional amount of noble metal has been used, however, the electrodes are suitable for uqe as anodes in fuel c~lls, with egually good operating characteristics and comparatively low costs o~ ~roduction.
It should be noted that electrodes according to the present inYention may be used as gas recombining electrodes in rechargeable alkaline zinc/manganese dioxide ~ells, as woll as in other primary or secondary alkaline cells. In particular, electrodes such as those described aboYe in Examples I to IV have utility as gas recombining .: - ,, - . . . ,-, ., WO91/20102 ~85~ PCT/CA91/00192 ~:
electrodes such as for oxyqen recombination in alkaline cells. The ability of such auxiliary porous electrodes to function at low temperatures and high current densities has been demonstrated.
The scope of this invention is defined in the accompanying claims. `:.
,,,, , - :
.. ........ . .... . .... .. . .. . .. .
FOR l~:LECTROC~EI~ I CAL CELLS, ~ND UETEIODS
OF ~AK I NG S~E
FI15LD OY THE INVENTION:
This invention relates to porou~ electrodes for fuel cells and similar cells such as air-metal cells, and alkaline zinc/manganese dioxide cells (particularly secondary cells), or other primary or secondary alkaline cells, and to the methods of making the present electrodes. In particular, the invention relates to porous electrodes which may be used a~ fuel cell cathodes or as auxiliary gas recombininy or transfer electrodes in alkaline cells, wherein a catalytically active layer i~
formed on a porous conductive substrate, and the catalytically active layer is derived from non-noble ~etals. In the event that the porous electrode is to be used as a fuel cell anode, a further small amount of a .. ,; ~.
noble metal is included in the catalytically active layer. ~.
In all events, electrodes according to the present invention have a lower loading of catalytically active .. ..,, ~, . . . . .
layer in terms of weight of catalyst per unit area of geometric electrode surface than heretofore, but with r r; ,~. , .
operating characteristics that compare favourably with prior art electrodes having noble metal catalysts, but being available at much reduced cost~.
., .. '' . ', ' ' ' . . ' " ~ ~ , ' . ', "' . , ~ , ,' ' ' ' ' ' ' .. , ' ' .. , ' ' ' ' ,.
.' ' ' ' ', . ' ', ~, . '. ' ' ' , . ' ,, ' , , , ", ~ .' ' ' , . . ' " ' , ' Wo91/20tO2 ` ' ~ ~8 ~ 3 ~ ~ PCT/CA91/OOt92 ~
. ., The present invention teaches several alternative methots for producing electrodes according to the present invention; whereby the electrode, once produced, will in all events have a catalytically active layer on a porous conductive substrate. Electrodes of the present invention may comprise a porous metal current collector, and a further gas diffusion layer, with the current collector being situated or embedded in the porous conductive ~ubstrate or within the gas diffusion layer.
J~CRGROIJND O~ T~l~ INVl~NTION:
The prior art has concerned itself, for many years, with the provision of porous electrodes that are particularly intended for use in fuel cells. However, while many ~uite acceptable electrodes have bcen provided in the prior art, it has been the general e~perience that ~uch electrodes are expensive to produce. This comes, especially, due to the generally accepted reguirement ~or the u~e of noble metals in fuel cell electrodes, including . ~ , .
especially gas diffu~ion or poro~s electrodes. Moreover, ; whén the prior art has provided electrodes ~hich comprise - , . - . - , . . .
a porous substrate having a porous catalytically active -, . . : ~ . . , layer theroon, it has been common in the past for there to be relatively high catalyst loading by weight per unit ,, . . :. ,. : ., , . .. . , . . i ar~a of ~eometrical electrode sur~ace, thereby contributing further to the cost of ~roducing such ' ' , ~ ` ', ~ ' ' ' . . ', ~ ' i ' ` .
WOsl/20102 ~ PCTtCA91/OOt92 20853~
electrodes.
Such prior art has included KORDESCH et al United States Patent 3,405,010 dated October 8, 1968, and XORDESCH United States Patent 3,310,434, dated March 21, 1967. The former patent relates to the catalyzing of porous electrodes, using a heavy metal salt, an aluminum salt, and a ruthenium salt. The latter patent is particularly related to the use of noble metals as catalysts on a porous electrode.
Yet another KORDESCH patent relating to the use of wet proofed conductive substrates having an active conductive layer with a surf?ce-deposited noble metal catalyst is United States Pa~cnt 3,899,354 issued August 12, 1975.
BARER et al in United States Patent 3,935,029 issued January 27, 1976 teach the use of fine graphite particles enmeshed in a web of polytetrafluoroethylene (PTFE), however, once again using noble metals.
Thus, it is a principal purpose of the present invention to provide catalyzed electrodes having excellent performance charac~eristics, at low cost. The catalyzed electrodes of the present-.invention are~-specifically ~dapted for use in fuel cells and metal-air cells; and especially u~eful as auxiliary gas recombining electrodes in alkaline zinc/manganese dioxide cells (particularly secondary cells), or-other primary or secondary alkaline -..
" . ~ '.' .~ ' ' ' ' ' ` ' . " ~ , 2 08 ~:3`~
cells. The porous catalyzed electrodes of the present invention have particular utility as oxygen reduction electrodes in alkaline cells as noted above.
Thus, the present invention comprises the provision of a porous electrode which comprises a porous conductive ~ubstrate and a porous catalytically active layer on the porous conductive substrate; the porous conductive substrate being chosen from the group consisting of carbon, graphite, and metal: and the porous catalytically active layer being chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, carbon, carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal. (If used as an anode in a fuel cell, the electrode of the present invention is as described above, together with a further additional smaller amount of a catalytically active noble metal or carbon together with a catalytically active noble metal.)-Catalytically active non-noble metals that are particularly ¢ontemplated for use in the present invention include iron, cobalt, nickel, manga~ese, chromium,-coppor, and vanadium: and catalytically active noble~metals there parki¢ularly.intended for~use in the present invention, in anodes according to this invention, include platinum, ~allædium, rhodium, iridium, osmium, gold, silver, and WO91/20102 2 0 8 5 ~ 5`: ~ PCT/CA91/00192 ruthenium.
In general, a porous electrode according to the .
present invention may include the porous active layer cho~en from the group consisting of carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal;
and very often, the porous active layer may further ~.
comprise polytetrafluoroethylene (PTFE3, as a binder. The t~`
carbon may be graphite.
Generally speaking, fuel cells may be considered to :~
be galvanic cells, with the basic reaction being the electrochemlcal oxidat.ion of a fuel and the electrochemical reduction of an oxidant (e.g., oxygen).
It should be noted, however, that fuel cells differ from ordinary primary cell9 ~uch a~ commercially available dry cells, in that tho fuel and o~idant are generally introducod continuously into the cell electrodes during the production of electricity. Thus, theoretically, the eloctrodes and electrolyte of fuel cells qhould maintain a constant value, during the time when the fuel and the o~idant are reacted electrochemically within the fuel cell, and-electricity and the. product of~ reaction --usually water -- ar- removed from the fuel cell.
~ ~ ~here ~has been, for the la t century or-so, a .continuing search for ways to boost the electrical output of fuel cell~, and/or to increa~e their ~ervice life, ~.
.:
, ~ .
Wo91/20102 2 0 8 ~ 3 ~ ~ ; PCT/CA91tO0192 .
and/or to lower the cost of producing fuel cells so as to render them commercially feasible. Needless to say, one major area for research has been the catalysis of reactions which take place within the electrodes of fuel cells, and thereby the requirement for discovering new methods of depositing known catalysts either in a more active form or more economically. However, the search still continues for catalysts which will raise the current density within electrodes, and/or the voltage of the cell, to levels which approach those that are attainable in theory.
On the other hand, .there has also developed a prsssing need for gas recombining electrodes in closed cells such as alkaline zinc/manganese dioxide cells --especially secondary c-lls. In such cells, there may be a periodic (or continuing) generation of gasses, and particularly there may be evolution of gaseous oxygen on charge, overcharge, or any reversal. of cell polarity.
Such cells typically operato over. a broad range of temperatures (e.g. from -40 to ~65 degrees Celsius) and at current densities where the auxiliary porous electrode may itself be reguired to pass up..to 7~0 mA/sg. cm.
It is the position of the present inventors that the present i~vention provides a major step..in:the.required direction, by providing.catalyzed porous condu~tors having relatively low production costs, and with excellent .. . .. .... .. . . ~ . . .. , . . .. . . , . ., .. . ,, .. .... .. . . ... ~ . .. .............. ... . ... . ... ..... .
. ... . .. .... . . .. . ...
wo gt/20l02 2 0 8 5 3 S ~ PcrtcAg1/00l92 . . . .
characteristics as to their efficiency, power density, performance, and life. The characteristics of electrodes according to the present invention compare most favourably with the characteristics of certain higher efficiency prior art fuel cell electrodes which, however, contained noble metals in all instances and which therefore were costly to produce.
When used as a catalyzed porous electrodes in fuel cells or alkaline zinc/manganese dioxide cells, electrodes of the present invention may comprise a porous gas tiffusion layer adhered to the porous conductive substrate spoken of above, at one side thereof. In fuel cells, electrodes according to the present invention may also generally include porous metal current collectors, as a conveniont way of conducting electrical current produced in the fuel cell out of the fuel cell.
In general, the catalyst provided by the present invention is insoluble within the operating voltage and the operating condition range of the electrode, thereby contributing to the life of the electrode. This means that-catalyzed porous electrodes according to the present invention may be used with such electrolytes as alkaline electrolytes,-for example potassium--hydroxide as used in zinc/manganese dioxide cell~s. It also makes the use of cataly~ed porous electrodes according to the present i~vention in mstal-air batteries and cells more . . . ~ . ,; :: , , ~ ~ .
. . . : . .,: . : . i . .
:-WO91/20102 2 ;0 8 5 ~ ~ 5 PCT/CA9t/00192 .- .
8 ;~
attractive. -. The inventors herein have discovered, guite unexpectedly, that the addition of a metal or metal oxide from the group consisting of iron, cobalt, nickel, manganese, chromium, copper, and vanadium -- all non-noble .
metals -- to a porous electrode provides an electrode having a service life and performance characteristics comparable to those of platinum catalyzed electrodes.
Clearly, the cost of electrodes according to the present invention, when compared to the cost of a platinum, catalyzed electrode, may be considerably lower. Moreover, platinum catalyzed electrodes may have significant carbon corrosion o~ the carbon within the porous substrate structure, whereas the use of metals and metal oxides according to the present invention significantly decrea~es the risk of carbon corrosion. That fact contributes, therefore, to the attractiveness of electrodes accordinq to the present invention for u~e in alkaline cell systems, and metal-air batteries. In addition, dissolved trace amounts of noble metals can cause problems in metal-air or other-batteries containing a zinc, iron or aluminum anode .. by.: enhancing the.hydrogen evolution (gassing;reaction).
.. This.enhanced. anode.corrosion cau~es high salf-discharge and can result in cell leakage.
According to the present invention, the porous conductive substrate of electrodes may be carbon, .-;
WO91/20102 2 0:8 3;3:S à PCT/CA91~00192 graphite, or metal; or, indeed, any other suitable conductive material. The porous active layer may comprise a catalytically active non-noble metal as discussed above, an oxide of a catalytically active non-noble metal, carbon, carbon toqether with a catalytically active non-noble metal, and carbon together with a oxide of catalytically active non-noble metal. Typically, the porous active layer consists of carbon together with a catalytically active non-noble metal or carbon together with an oxide of catalytically active non-noble metal; and in either case, it may further comprise a binder, usually PTFE.
A typical porous electrode accordlng to the present invontion would consist of an electrochemically active layer which may be typically from 50 to 500 microns thick, and it may further include a gas diffusion layer which may also be 50 to 500 microns thick. If used in a fuel cell, the clectrode would usually also have a metal scroen current collector (a porous metallic current collector) embedded in an electrode layer -- unless a bipolar 'con~truction method is applied. The electrochemically active~'layer,-as noted,'-would contain the electrocatalyst as described'àbove,'supported on ~ carbon, graphite or 'metal''porous~sub~trate,~"and''is located on the electrolyte side of the electrode.
A gas diffusion layer, when used, may typically .. . .. .. . . . . . .. .. . . . . .. . . . .. ..... ..... . . .... .. . . ........ . .. . ..
WO91/20102 2 0 8`~ 3:~ ~ PCT/CA91/00192 consist of PTFE bonded carbon, and would normally have a higher degree of hydrophobicity than the active layer.
During the manufacturing process of the gas diffusion layer, discussed in greater detail hereafter, a pore builder such as ammoniumbicarbonate, may be used. The current collector, when used, may be embedded in either the gas diffusion layer or the active layer; and when electrodes according to the present invention are used in bipolar cells, no current collector is reguired.
Typically, the total electrode thickness of an electrode comprising an active layer, a gas diffusion layer, and a current collector, may range from ioo to 750 microns.
Thus, porous olectrodes according to the present invention may comprise a porous conductive substrate, and a porous gas diffusion layer adhered to one side thereof.
As notcd, the porous active layer is at a first side of the porous conductive substrate, and the porous gas dif$usion layer is at the ~ide of the porous conductive substrate opposite to that of the active layer. Of course, the porous active layer may permeate the porous conductive substrate, and in any event the porous gas diffusion layer i adhered to one side thereof. ,-~ - ~s noted above, electrodes according to the present - invention may also ~e used as anodes in fuel cells, in which ~ase a further additional smaller amount of a .. .. . . . .. . . . ... . ... . . . ... .
~Q~3~
catalytically active noble metal or carbon together with a catalytically active noble metal is added to the catalytically active layer of the electrode. There is little point in providing oxides of catalytically active noble metals, since the oxide would be promptly reduced to the noble metal per se when exposed to the hydrogen fuel generally used ih a fuel cell.
The noble metals contemplated for use in this aspect of the invention are discussed above.
The concentration of catalyst within the porous catalytically active layer is generally in the range of from O.l to lO mg per sguare centimeter of the gèometrical electrode surface area. Typically, the concentration of catalyst wit~in the porous catalytically active layer is in the range of from l to 5 mg per square centimeter of the geometrical electrode surfac0 area.
In general, cathodes for hydrogen/oxygen fuel cells, according to the preqient invention, may have a service life well in excess of two thousand hours at a current density of lO0 mil1iamperes per siquare centimeter, at a voltage above 0.85 volts--versus RHE (Reversible Hydrogen Electrode). Similar electrodes, using non-noble metal oxide catalysts, can be run at up to 300 mil?iamperes per .. . .... ... .. . . . ..
s~uare centimeter on oxyg~n and air, with potentials of about 0.8 volts and 0.79 volts versus RHE, respectively.
As auxiliary gas recombining electrodes used in alkaline - . : .: , ~ , , ,- .,. : . . . . . .
, ; ~ , ~ ; . - .:
W O 9t/20102 2 0 8 5 3 5 ~ P~r/CA91/00192 `
electrochemical cells such as zinctmanganese dioxide cells having potassium hydroxide electrolytes, the electrodes may be successfully subjected to current densities up to 7~0 m~/sg. cm. at low temperatures.
The present invention provides three generally related but tistinct processes for the production of porous electrodes in keeping herewith. Those three general methods may be characterized a~ follows:
I (a) impregnating a porous conductive substrate structure with a compound containing the chosen material for the porous catalytically active layer; and (b) forming the porous catalytically active layer:
II (a) mixing the chosen material for said porous catalytically active layer with the chosen material for the porous conductive substrate;
and (b) fabricating the electrode:
III (a) depositing pyrolytic carbon from the gas phase -onto a porous conductive substrate structure, at an elevated temperature in a gas atmosphere.
The compound used in step (a) of Process I, above, is - : . .
a metal salt solution of thè chosen catalytically active .. . .
metal. The formation process of step (b) of the Process I
may be the chemical formation of the porous active layer, or the thermal formation of the porous active layer.
.. ~ ... .... , ,.: .. ....... .. . . .... ..
, . . . .. . .. .
W O 91/20102 . P~r/CA91/00192 2~8~3~5 ` "
~he chosen active material that is used in step (a) of the Process II, may further be mixed with carbon and ~ ,7'!' PTFE. , The Process III is carried out at least 600 degrees ' C, and the gas atmosphere may be steam, carbon dioxide, ' "
carbon monoxide, ammonia, nitrogen, argon, or hydrogen. ' ".
~RIEF DESCRIPTION OF THE DRAWINGS:
A typical embodiment of the present invention when used as an auxiliary electrode as an oxygen gas recombining electrode in an alkaline zinc/manganese dioxide cell is shown in the singlo Figure of drawing which accompanies the following di~cusslon.
DETAILE~ DESCRIP~ION OF THE ~REFERRED EMBODIMENTS: j'.
The Figure shows a typical cmbodiment of an alkaline zinc/manganese dioxide cell having an auxiliary porous o~ygen ga~ recombining electrode in koeplng with the ' present invention. The cell comprises a steel can 10 having a :conventional.metal oxide cat~ode 12 which is typically fonmed cylindrically around an anode 14. The cathode`l'2'.may.comprise ~inely.divide&.manganese dio~ide '-' and 'gr~phite,-:and the anode. ~ay~compri~e zinc powder.
Between the cathode and the anode is an .electrolyte ' .
permeable separator 16; When the cathode is manganese~ ~' dio~ide and the anode is zinc, then the electrolyte may be an aqueous 301ution of potassium hydroxide. A boss or a .
.. . . . .... .. . . . .. .. . . . . ..... . .... .. . . . . . .. . ... . .
W O 91/20102 PC~r/CA91/OOt92 2`~`g~)35~ ` , .
.
pip 18 is ~ormed at the base of the can 10, to give the cathode or positive contact for the cell.
The electrolyte permeable separator 16 is typically formed of rayon/polyvinyl alcohol. The anode may have at its upper end an auxiliary porous gas recombining electrode 20, which is arranged so as to be wetted by the electrolyte. At its lower end, the anode may be provided with an insulated disc or basket 22, to preclude anode contact with the cathode pip 18.
A current collector nail 24 projects into the anode 14 through a casing cover 26, with the head 28 of the collector nail 24 being on the outside of tho cover 26 to form the anode contact ~or the cell. The cover 26 seals the can 10 by crimping formed around its edge. An additional anode cover 30 i~ provided to give the anode or negative contact for the cell.
The cathode may be provided with auxiliary cathode material to catalyze the reabsorption of hydrogen as set forth in KORDE5CH and TOMANTSCHGER United States Patent 4,925,747 issued May 15, 1990. The ausiliary eloctrode 20 may have the characteristics set forth in TOMANTSCHGER and --KORDESCH United States Patent 4,900,642 issued February 13,-1990. ~
- There follo~ several examples of various electrode -structures according to the present invention, their ~anufacture, and their operating characteristics, ... ... ~. ~.................. .
,~: . . , . - , ,, , .
.. - . , -WO 91/20102 PCltCA9ltOOt92 2'~ 3 5 a' `' ''"
~XAMPLE I:
Under the general steps of Process I noted above, a graphite felt (for example, a graphite product available commercially as PANEX~ CFP 30-10) was impregnated with manganose nitrate solution and pressed into a layer which comprised a mixture of carbon available commercially as SHAWINIGAN BLACRT~ and PTFE. The carbon/PTFE layer comprised 62.5% carbon, 37.5% PTFE.
The catalyst was thermally formed at 300 degrees C, in air, a~d resulted in an electrode having catalyst loading of 1.5 mg. of manganese per sguare centimeter of - :
geometrical electrode surace area. The following table demonstrates the electrode p¢rf ormance, as a cathode at the oxygen side of an o~ygen/hydrogen fuel cell system having 9 N ~OH electrolyte, at 65 degrees C.
Current Density IR free potential ~mA/s~.cm.~ [mV vq. RHE]
(~he IR free potential is determined using laboratory proc~dures a~d standards, and is measured in millivolts as ... , . . . , ., . . .. , ..... , ........ .. ...... ,, .. ... .. , .. ,, .,~. .... ,., .. ~, .. .. . . . ... . . ... .. .. ....
. . ... . .. . .
W O 91t20102 2 a 8 5 3 ~ ~ PC~r/CA91/00192 :: " . ` I
against a Reversible Hydrogen Electrode reference).
~X~hE II:
Again, using the general Process I, an active layer of nickel FIBREX~ felt was impregnated with manganese nitrate solution, and again pressed into a carbon/PTFE
layer as in Example I. The catalyst was thermally formed at 300 degrees C in air, with a catalyst loading of 7.6 mg. of manganese per square centimeter of geometrical electrode surface area.
The electrode performance in an oxygen/hydrogen fuel cell system, having 6 N ~OH electrode, at 20 degrees C, was as foll GWg: :
Current Density IR free potential ~mA/sq.cm.~ tmV vs. RHE]
150 764 ;
~AMP~
In thi~ case, activated carbon plus an active catalyst waq used, in a multi-layer PTFE bonded carbon electrode. .The gas diffusion layer was a carbon~PTFE
layer as described above in Examples I and II.
The active layer comprised carbon black available commercially as VULCANIM XC 72R which was acti~ated to 30%
weight loss in the ~resence of cobalt-aluminum spinel (5 SUBST~TUT~ SHI~
.. . . . . ..
,.' 1 . '. ' ' . ' . , , . ~,.. .. ~ : ' ' ' ' ' . .. ' . ' ... . . ~ . . ..... , . . .. ~ .. :
~ . .... ... - .... . : - :-. ~ . . ' . , - ~, . .
W O 91/20102 2 b 8 5 3 s ~ PC~r/CA91/00192 mmol cobalt, 10 mmol aluminum per 100 grams of carbon), in the amount of 67~ together with graphite in the amount of 22~, and PTFE in the amount of 11%.
The catalyst loading was 5 mg. of manganese dioxide per square centimeter of geometrical electrode surface area, which may also be expressed as 3.2 mg. of manganese per s~uare ~entimeter of geometrical electrode surface area.
The electrode was operated for 220 hours at 100 milliamperes per square centimeter at 65 degrees C in 12 N
KOH. The oxygen and air operation, both, of thé electrode are set forth in the ~ollowing table:
Current Density IR free potential IR free potential ~mA/sg.cm.~ ~mV vs. RHE~ ~mV vs. RHE~
Oxygen Air .....
The electrode wa~ also operated at 150 milliamperes per square centimeter, over a varying range of tomperatures, with air operation being observed as set .... . .. , . . . . . . ...................... . , . ,. , . ~ . . . . . .
-: .
- . : . - : ,; . ... . . .
. ., ,. ,. , ., . . ::
WO9lt20102 2 0 8 5 3 ~ j PCT/CA91/00192 forth in the following table. . -Temperature IR free potential at 150 mA/cm ., tc~ Air operation ~mV vs. RHE]
6~ 834 737 ~.
Finally, oxygen long term performance in 12 N KOH at 65 degrees C, operating at 100 milliamperes per square centimoter, was determined as follows:
Oxygen long term performanco in 12 N K~H at 65 C and 100 mA/cm.l~1 .
time IR free potential at 100 ma/cm ~hrs] ~mV vs. RHE~
500 893.
1000 . 890 lS00 ` 851 .. ~
-. . . . . - ., -~: ~ :
Under the Process III, VULCANTN XC 72R carbon was activat~d in the presence of 5 mmol of cobalt per 100 ',.
-~ WO91/20102 2 0 8 ~ 3 5 S PCT/CA91/00192 `' .:
grams of carbon in the gas phase, in a carbon dioxide ~as atmosphere, at lO00 degrees C. This resulted in an active layer consisting of carbon activated at lOOO-C in carbon dioxide atmosphere, in the amount of 95.2% containing cobalt oxide; with PTFE in the amount of 4.8%
The catalyst loading was determined to be l.3 mg. of cobalt per square centimeter of geometrical electrode sur$ace area.
The electrode performance was determiner in 9 N XOH, at 20 degrees C with oxygen, as follows:
Current Density IR free potential ~mA/sq.cm.] tmV vs. R~E~
0 gO5 l 832 lO0 755 lS0 725 E:Xl~MPLE V:
Along the general lines of preparation of an electrode in keeping with Example II, an anode was fabricated, as follows:
The gas dlffusion layer comprised carbon (SHAWINIGAN
BLACK) in the-amount of 50%, with 50% PTFE.
The actiYe layer comprised superconductive carbon bla~ available commercially as BLACK PEAR~S~ activated , . . , , . .~; . : , WO 91/20102 ~ 2 0 8 ~ 3 5 ~ PCT/CA91/00192 " .
to 30% weight loss in the presence of cobalt-aluminum spinel (5 mmol cobalt, 10 mmol aluminum per 100 grams of carbon), together with ruthenium (0.2 grams Ru per 100 grams of carbon) all in the amount of 80~; with 20% PTFE.
The following table demonstrates the performance of this electrode, as an anode, after 165 hours at 100 milliamperes per square centimeter at 65 degrees C in 12 N :-XOH, with hydrogen:
Current Density IR free potential tmA/sq.cm.] tmV vs. RHE]
O
150 15 `.
Opcration at 150 milliamperes per sguare centimeter over a range of temperatures, resulted in the following: :
:
Temperature IR free potential at 150 :
mA/cm ~C] tmV vs. RXE]
23 .
. 23 ' ~ 565 . - . 26 ~5 36 i:~
; - 40 ` 43 .
;
.- . ....... , - - - . . . . :
W091/20102 2 0 8 ~3S 5 PCT/CA91/OOt92 . ~
Finally, hydrogen long term performance in 12 N KOH ";-at 65 degrees C and lOO milliamperes per square centimeter was determined, with the following results:
timeIR free potential at lOO mA/cm ~hrs] ~mV vs. RHE3 10 .j lOO 39 500 ~S
lOOO 49 lSOO 83 2000 lO9 There have been described 0lectrodes that are ~ntended ~or use as cathodes in fuel cells (or metal-air cells), or as auxiliary gas recombining electrodes in sealed alkaline cells, which electrodes have excellent operatiny characteristics and which are produced without the requirement for use of noble metals. When a small additional amount of noble metal has been used, however, the electrodes are suitable for uqe as anodes in fuel c~lls, with egually good operating characteristics and comparatively low costs o~ ~roduction.
It should be noted that electrodes according to the present inYention may be used as gas recombining electrodes in rechargeable alkaline zinc/manganese dioxide ~ells, as woll as in other primary or secondary alkaline cells. In particular, electrodes such as those described aboYe in Examples I to IV have utility as gas recombining .: - ,, - . . . ,-, ., WO91/20102 ~85~ PCT/CA91/00192 ~:
electrodes such as for oxyqen recombination in alkaline cells. The ability of such auxiliary porous electrodes to function at low temperatures and high current densities has been demonstrated.
The scope of this invention is defined in the accompanying claims. `:.
,,,, , - :
.. ........ . .... . .... .. . .. . .. .
Claims (13)
1. An alkaline electrochemical cell haing a cathode, an anode, an alkaline electrolyte, and a porous electrode for use as an oxygen reduction electrode when said electrochemical cell operates at current densities up to 750mA/sq.cm.;
wherein said porous electrode comprises a porous conductive substrate and a porous catalytically active layer on said porous conductive substrate;
wherein said porous conductive substrate is chosen from the group consisting of carbon, graphite, and metal; and wherein said porous catalytically active layer is chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal.
wherein said porous electrode comprises a porous conductive substrate and a porous catalytically active layer on said porous conductive substrate;
wherein said porous conductive substrate is chosen from the group consisting of carbon, graphite, and metal; and wherein said porous catalytically active layer is chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal.
2. The alkaline electrochemical cell of claim 1, wherein said catalytically active non-noble metal is chosen from the group consisting of iron, cobalt, nickel, manganese, chromium, copper, and vanadium.
3. The alkaline electrochemical cell of claim 2, wherein said porous catalytically active layer is chosen from the group consisting of carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal;
and said porous catalytically active layer further comprises polytetrafluoroethylene (PTFE) as a binder.
and said porous catalytically active layer further comprises polytetrafluoroethylene (PTFE) as a binder.
4. The alkaline electrochemical cell of claim 3, wherein said carbon component is graphite.
5. The alkaline electrochemical cell of claim 1, wherein said anode is zinc, said electrolyte is potassium hydroxide, and, said cathode is manganese dioxide.
6. An alkaline electrochemical cell having an anode, an alkaline electrolyte, a cathode, and a further porous electrode for use as a gas recombining electrode;
wherein said porous electrode comprises a porous conductive substrate and a porous catalytically active layer on said porous conductive substrate;
wherein said porous conductive substrate is chosen from the group consisting of carbon, graphite, and metal; and wherein said porous catalytically active layer is chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal; and wherein said gas recombining electrode recombines oxygen generated within said cell.
wherein said porous electrode comprises a porous conductive substrate and a porous catalytically active layer on said porous conductive substrate;
wherein said porous conductive substrate is chosen from the group consisting of carbon, graphite, and metal; and wherein said porous catalytically active layer is chosen from the group consisting of a catalytically active non-noble metal, an oxide of a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal; and wherein said gas recombining electrode recombines oxygen generated within said cell.
7. The alkaline electrochemical cell of claim 6, wherein said anode is a zinc anode, said alkaline electrolyte is potassium hydroxide, ant said cathode is manganese dioxide.
8. The alkaline electrochemical cell of claim 7, wherein said cell is a secondary cell.
9. The alkaline electrochemical cell of claim 6, wherein said porous catalytically active layer is chosen from the group consisting of carbon together with a catalytically active non-noble metal, and carbon together with an oxide of a catalytically active non-noble metal;
and said porous catalytically active layer further comprises polytetrafluoroethylene (PTFE) as a binder.
and said porous catalytically active layer further comprises polytetrafluoroethylene (PTFE) as a binder.
10. The alkaline electrochemical cell of claim 9, wherein said carbon component is graphite.
11. The alkaline electrochemical cell of claim 1, wherein said anode is chosen from the group comprising iron and aluminum.
12. The alkaline electrochemical cell of claim 2, wherein the concentration of catalyst within the porous catalytically active layer is in the range of 0.1 to 10 mg/cm of the geometrical electrode surface area.
13. The alkaline electrochemical cell of claim 12, wherein the concentration of catalyst within the porous catalytically active layer is in the range of 1 to 5 mg/cm of the geometrical electrode surface area.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US540,932 | 1990-06-15 | ||
| US07/540,932 US5069988A (en) | 1987-08-24 | 1990-06-15 | Metal and metal oxide catalyzed electrodes for electrochemical cells, and methods of making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2085355A1 true CA2085355A1 (en) | 1991-12-16 |
Family
ID=24157509
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002085355A Abandoned CA2085355A1 (en) | 1990-06-15 | 1991-05-31 | Metal and metal oxide catalyzed electrodes for electrochemical cells, and methods of making same |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0533711A1 (en) |
| JP (1) | JPH06500659A (en) |
| CA (1) | CA2085355A1 (en) |
| WO (1) | WO1991020102A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6780347B2 (en) * | 2002-02-04 | 2004-08-24 | Rayovac Corporation | Manganese oxide based electrode for alkaline electrochemical system and method of its production |
| EP2728641B1 (en) * | 2012-10-31 | 2017-02-22 | Saft | Low maintenance alkaline electrochemical cell |
| WO2019133702A1 (en) | 2017-12-29 | 2019-07-04 | Staq Energy, Inc. | Long life sealed alkaline secondary batteries |
| JP2021533552A (en) | 2018-07-27 | 2021-12-02 | フォーム エナジー インク | Negative electrode for electrochemical cell |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1306284C (en) * | 1987-08-24 | 1992-08-11 | Karl V. Kordesch | Metal and metal oxide catalyzed electrodes for electrochemical cells, and methods of making same |
| HU208596B (en) * | 1987-10-27 | 1993-11-29 | Battery Technologies Inc | Rechargeable electrochemical cell |
-
1991
- 1991-05-31 EP EP91910310A patent/EP0533711A1/en not_active Withdrawn
- 1991-05-31 CA CA002085355A patent/CA2085355A1/en not_active Abandoned
- 1991-05-31 JP JP3509492A patent/JPH06500659A/en active Pending
- 1991-05-31 WO PCT/CA1991/000192 patent/WO1991020102A1/en active Search and Examination
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06500659A (en) | 1994-01-20 |
| EP0533711A1 (en) | 1993-03-31 |
| WO1991020102A1 (en) | 1991-12-26 |
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