CA1077559A - Electrochemical generator with passivated electron collector - Google Patents
Electrochemical generator with passivated electron collectorInfo
- Publication number
- CA1077559A CA1077559A CA257,750A CA257750A CA1077559A CA 1077559 A CA1077559 A CA 1077559A CA 257750 A CA257750 A CA 257750A CA 1077559 A CA1077559 A CA 1077559A
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- electrochemical generator
- generator according
- suspension
- particles
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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
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/22—Fuel cells in which the fuel is based on materials comprising carbon or oxygen or hydrogen and other elements; Fuel cells in which the fuel is based on materials comprising only elements other than carbon, oxygen or hydrogen
- H01M8/225—Fuel cells in which the fuel is based on materials comprising particulate active material in the form of a suspension, a dispersion, a fluidised bed or a paste
-
- 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
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
-
- 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
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/661—Metal or alloys, e.g. alloy coatings
-
- 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
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/669—Steels
-
- 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)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Life Sciences & Earth Sciences (AREA)
- Dispersion Chemistry (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Hybrid Cells (AREA)
- Inert Electrodes (AREA)
- Fuel Cell (AREA)
- Cell Electrode Carriers And Collectors (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
An electrochemical generator formed of at least one cell comprises, on the one hand, at least one anode compartment containing a suspension of active metallic particles in an elec-trolyte and having an electron collector, and, on the other hand, at least one cathode compartment having a cathode with an active material. In accordance with the invention the surface of the said electron collector facing the suspension is made of a metallic material which is in passivated state.
An electrochemical generator formed of at least one cell comprises, on the one hand, at least one anode compartment containing a suspension of active metallic particles in an elec-trolyte and having an electron collector, and, on the other hand, at least one cathode compartment having a cathode with an active material. In accordance with the invention the surface of the said electron collector facing the suspension is made of a metallic material which is in passivated state.
Description
1077~i;59 The present invention relates to electric current generators operating by electrochemical oxidation and formed of at least one cell having an anode compartment and a cathode compartment, or a plurality of said compartments.
The invention is particularly concerned with such gene-rators in which the active material of the anode compartment, at times referred to as the fuel, is a metallic material.
When such a generator delivers electric current into a discharge circuit, the said active metallic material under-goes electrochemical oxidation in the anode compartment, losingelectron$, while the active material of the cathode compartment is reduced by the electrons coming from the anode compartmen-t via the intermediate discharge circuit.
It is already known to use the said active metallic material in the form oE a suspension of particles in an electro-lyte. The said active metallic particles then lose electrons in contact with an electrically conductive electron collector in the anode compartment, in particular a metallic electron collec-tor. However, when the said active metallic particles are in permanent contact with the electron collector, products result-ing from their oxidation accumulate frequently on or near their sur~aces. This ~esults in a passivating o~ the said active metallic particles, which makes their complete oxidation impos-sible.
It has been attempted to avoid this drawback by circu-lating the said suspension of active metallic particles in the anode compartment in such a manner that the active metallic par-ticles are in intermittent contact with the said electron collec-tor.By alternately feeding the active metallic particles into contact with the electron collector and removing them from same, the diffusing of the oxidation products-throughout the electro-lyte is favored.
. ' '. . , ' .
~L07~75S9 The passivation is furthermore retarded by circulating said suspension of active metallic particles outside of the anode compartment and recycling it into said anode compartment so that the active metallic particles again participate in the discharge reaction.
Actual practice shows that such generators can give acceptable results for experimental cells. On the other hand, in cells suitable for industrial applications, for instance for the driving of vehicles, namely in cells capable of provid-ing a ï ela-ti-~el~ large amount of power, active metallic parti-cles attach themselves to the surface of the electron collector when the latter is metallic, whatever the means used to move or recycle the suspension. These particles which are attached to the surface oE the electron collector cause an agglomerating of the other particles in suspension in the electrolyte. This agglomeration is propagated in the anode compartment. It may lead to obstruction of said compartment and considerably reduce the power of the cell as a result of the passivating of the agglomerated particles. This agglomeration can take place even when the suspension is circulated without the cell delivering current.
The properties o the elements forming the electro-chemical generator of the type to which the invention applies which affect the attaching and the agglomerating of the said particles seem to be very diversified and concern only the com-ponents of the anode compartment, in particular: physical pro-perties and constants of the material forming the surface of the collector; chemical and electrochemical behavior of the collector and of the active metallic particles and electrolyte;
liberation of gases.
The object of the present invention is to provide a collector and therefore a generator which are free of the ~77~59 above-indicated drawbacks.
Accordingly, the invention as herein broadly claimed is an electrochemical generator formed of at least one cell comprising, on the one hand, at least one anode compartment containing a suspension of active particles, formed at least in part of zinc, in an aqueous alkaline electrolyte and having an electron collector, the suspension circulating through the anode compartment in such a manner that the particles undergo intermittent and repeated contacts with the electron collector, and, on the other hand, at least one cathode compartment having a cathode with an active material, and characterized by the fact that the surface of the electron collector facing the suspension is make of a metallic material which is covered by a passivating layer, the layer containing at least one inorganic compound of at least one metal constituting at least in part the metallic material, the metal being selected from the group consisting of magnesium, scanaium, yttrium, lanthanum, titanium, zirconium, hafnium, niobium, tantalum and chromium.
This passivating layer, which is formed, for instance, when the electron collector is in contact with atmospheric air or the electrolyte, is indestructible by -the electrolyte and the anodic.suspension. This layer prevents direct contact of the anodic metallic particles with the metal material of the surface of the collector. The said inorganic compounds may, for instance, be salts, oxides, or hydroxides.
The metallic materials which can give rise to such passivation phenomena are, in particular, magnesium, metals of Groups IIIB, IVB, VB and VIB of the periodic classification of elements (Handbook of Chemistry and Physics, 53rd Edition, 1972-1973, published by the Chemical Rubber Co., of Cleveland, Ohio) and, more particularly, scandium, yttrium, lanthanum, titanium, zirconium, hafnium, niobium, tantalum, and chromium, ~ :~C377559 .:
or some of their alloys with each other or with other metals.
By active metallic particles of the anode compartment, there are understood particles formed in whole or in ~t - 3a -... . ..
~q37~5~9 active anodic material, for instance, particles the electroche-mically inactive center of which is covered with a shell formed of the active anodic material.
In accordance with preferred features of the invention:
a) the metallic material of the surface of the collec-tor consists of chromium or titanium;
b) the chromium is deposited electrolytically on an electron-conducting support, for instance a support of metal, or, when it is desired to produce collectors which are particularly light and/or of complicated shape, of a plastic material which has been made a conductor of electrons throughout or as a result of a coating;
c) -the anodic metallic particles are particl.es of zinc, d) the electrolyte .is an alkaline electrolyte, e) the active material o the cathode is oxygen or a compound of oxygen, for instance a metallic oxide, f) the anodic suspension is arranged in the cell between the cathode compartment and the anodic electron collector, g) a hydrophilic separator which is a non-conductor of electrons, is permeable to the electrolyte and to -the ions, and .is impermeable to the anodic particles is arranged between the anode compartment and the cathode compartment in orcler to prevent said particles from coming into contact with the electron-conduc-tive zones of the cathode, which would cause short circuits, h) the cell comprises a means for feeding and a means for discharging the said suspension, a means for the recycling and/or regenerating of the said suspension being possibly arranged between the discharge means and the feed means.
The invention will easily be understood from l:he follow-0 ing non-limitative example:
A zinc/air generator of a power of abo~t 50 watts, a diagrammatic cross sec-tion of which is shown in the accompanying ~L~'77559 drawing, is formed of a cell (1~. This cell (1) comprises a positive terminal and a negative terminal (which are not shown) connected by an electric discharge circuit (not shown). The essential elements of this cell (1) are arranged in the follow-ing manner:
In the cathode compartment (2) there can be observed the cathode, which is an air-diffusion electrode (21), the ca-thode active material being oxygen (flow of air not shown). This cathode (21) is formed, in known manner, essentially of carbon, silver, polytetrafluorethylene and nickel. This electrode (21) is covered on its surface (211) by a hydrophilic separator (3) which is a non-conductor of electrons, is permeable to ions and to the elec-trolyte, and is impermeable to the particles oE
æinc (~1). Facing the separator (3) there is arranged an anodic electron collector (42), which is a conductor of electrons, and is impermeable to the electrolyte, the ions and the zinc parti-cles.
The space between the surface (421) of the anodic elec-tron collector (42) and the separator (3) constitutes the anode compartment (4).
The cell (1) comprises at one end (5) a device (not shown) ~or the feeding of a suspension of zinc particles (41) in an electrolyte and at the other end (6) a device ( not shown) for discharging said suspension.
A device (7) makes it possible to circulate the suspen-sion in the anode compartment (4) and recycle it into said anode compartment via a system (8) which is external to the anode compartment. This external system comprises a feed device (81) which makes it possible to maintain the percentage by weight of zinc in suspension in the electrolyte constant, and a buffer reservoir (82~ of sui-table volume.
The particles (41) circulating in the anode compar-tment .
undergo intermittent and repeated contacts with the surface (421) of the anodic electron collector (42) during their passage through the cell.
The electrolyte consists of 6N potassium hydroxide ( 6 mols of KOH per liter) and the average diameter of the zinc particles (41) is 10-20 microns.
Such a cell ~1) serves for the carrying out of compara-tive operating tests with anodic electron collectors (42) whose surface (421) facing the suspension is made with different metals or alloys.
During each test, on the one hand, the intensity of the discharge current of the cell (1) is maintained constant, or instance equal to 150 mA per cm2 oE active surface (211) of the air electrode, and, on the other hand, the percentage by weight of zinc particles (41) in suspension in the electrolyte is maintained at a constant value of between 10% and 30% of the weight of the electrolyte. Furthermore, the circulating of the suspension in the cell ( 1) is effected with constant speeds of between 15 m/min and 30 m/min.
During the operation of the generator, the temperature of the electrolyte and of the anodic electron collector (42) remains substantially equal to ambient temperature (about 25C).
At the beginning of each test, the concentration of zinc dissolved in the form of potassium zincate in the electro-lyte is zero.It increases gradually during the discharge and when it reaches about 120 g/liter, beyond which value the particles of the anode suspension become practically inactive, the zincated electrolyte of the anode compartment ~4~ and of the system (8) is replaced by a fresh 6N potassium hydroxide solution free of potassium zincate and the test is contlnued by proceeding with a new discharge.
The metals or alloys used to produce the suriace (421) 6 ~ r ~L~7755~
of the electron collector ~42) belong to the following three groups:
A. Copper, nickel, iron, leadl used in the form of metal sheets;
~ cadmium used in the form of electrolytic deposit on a nickel sheet support;
- platinum, rhodium, gold, silver, used in the form of electrolytic deposits on a copper sheet support.
B. Titanium used in the form of a metal sheet;
- chromium used in theIform of electrolytic deposits on copper and brass sheet supports.
C. Stainless steel corresponding to the designation AFNOR Z6CNl~-09 tabout 0.07~ carbon, 17~ to 19~ chrom:ium, 8~ to 10~ nickel);
- stainless steel corresponding to the designation AFNOR Zl NCDU 25-20-4-2- ( at most 0.02~ carbon, a~ou-t 24~ to 27% nickel, 19~ to 22% chromium, less than 2% manganese, 4% to 4.8% molybdenum, 1% to 2% copper);
-stainless steel type ORION 26.1 oE the Societe Creu-sot-Loire (abou-t 0.002~ carbon, 26% chromium, 1~ molybdenum);
these three steels being used in the form of sheets.
The supports on which the electrolytic deposits are effected (groups A and B) are used in non-annealed and in an-nealed condition.
Experiment shows that the maximum voltages of the ge-nerator are obtained at the start of the tests, when the concen-tration o~ zinc dissolved in -the electrolyte in the form of po-tassium zincate is low.
Furthermore, the highest maximum voltages are produced when the rate of circulation is the lowest and the concentration of zinc particles the highes-t.
For a ra-te of circulation of 15 m/min, a current of ~7~55~ ~ !
150 mA per cm of active surface (211) of the air electrode and a concentration of zinc particles of 30~, the maximum ~oltages expressed in volts of the generator are substantially as follows, as a function of the different metallic materials used for the surface (421) of the collector (42):
A. Copper: 1.06 V; cadmium: 1.06V; nickel: 1.04V; iron:
0.95V; platinum: 1.06V; rhodium: 1.07V; gold: 1.03V; silver:
1.00V; lead: 0.98V;
B. Chromium on copper or brass, not annealed: 00875V;
chromium on copper or brass, annealed: 1.05V; titanium: 0.85V;
C. Stainless steel Z 6CN 18-09: 0.915V; stainless steel Z 1 NCDU 25-20-4-2: 0.91V; stainless steel ORION 26.1: 0 750V.
With respect to the attachment o~ the zinc part:icles to the surface (~21) of the collector (~2) and their aggLomera-tion, the following has been noted:
When the surface (421) of the collector (42) is made of one of the metals of group A or of the stainless steels Z 6 CN 18-09 and ORION 26.1 of group C, zinc particles attach themselves to the surface (421) of the collector (42) and form agglomerates. This takes place before the end of the first discharge has been reached, that is to say before the concentra-tion oE zinc dissolved in the electrolyte reaches the maximum permitted value of 120 g/liter. If the test is contlnued, the anode compartment (4) gradually becomes clogged. Circulation of the suspension of particles becomes impossible, whatever the device used to effect the circulation. At the same time, the voltage of the generator decreases rapidly and becomes practi-cally zero as a result of the accelerated passivation of the agglomerated particles. The generator thus becomes unusable upon the first discharge, whatever the weight of zinc in suspension in the electrolyte, the rate of circulation of the suspension, and the intensity of the discharge current.
~77559 When the surface (421) of the collector (42) is made of one of the metals of group B or of stainless steel ~ l NCDU
25-20-4-2 of group C, no attachment of the anodic particles to the collector takes place and no agglomeration, whatever the weight of zinc in suspension in the electrolyte, the rate of circulation of the suspension, and the intensity of the dischar-ge current.
If it happens that particles should momentarily become immobilized at the collector, they are again placed in circula-tion shortly afterwards without forming agglomerates. Moreover, the uniform decrease of the voltage of the generator caused by the increase in the zincate content of the electrolyl;e is rela-tively small, of the order of 10~ as compared with the maximum voltage at the start of discharge for an intensity of the discharge current equal to 150mA per cm2 of active surface of the air electrode. It is sufficient to renew the 6N potassium hydroxide solution when its concentration of dissolved zinc reaches the limit value predetermined for effecting repeated discharges.
As a matter of fact, the operation of the generator i5 limited only by the life of the air electrode. This life may easily exceed several hundred discharges. The same result can be obtained if, instead of renewing the electrolyte when its concentration reaches a predetermined limit value, a con~inuous regeneration of the electrolyte is effected in an attached de-vice.
Metals of group A are not is passivated sta-te under the conditions of the test. Metals of groups B, that is to say chromium and titanium, are on the other hand passivated in con-tact with the air or the electrolyte under the condit:Lons of the experiment, their surface becoming covered with a layer formed primarily of higher or lower hydrates of oxides of these metals.
g _ 1~77559 This test, therefore, shows -that the presence of this passivating layer avoids the attachment and agglomeration of the zinc particles on the surface of the collector. This pheno-menon apparently could be attributed to a modification of the electrochemical behavior of the combination formed by the surface of the metallic collector, the electrolyte, and the anodic sus-pension. Likewise, the difference in the results obtained with the three types of stainless steels (group C , all of which con-tain chromium in an amount theoretically suf icient to obtain on the surface of the collector a passivating film of higher or lower hydrates of chromium oxides can apparently be attributed to the following facts. On the one hand, the austenitic steel Z 6 CN-18-09, contrar~ to austenitic steel ~1 NCDU 25-20-~-2, i5 thermodynamically unstable a-t the low temperatures of use of the generator, these temperatures being generally between 20C.
and 60C., and its percentage of carbon is relatively high, which two factors may result in a break in passivity of the surface.
On the other hand, steel ORION 26.1, since it is ferritic, is more sensitive to the break in passivity of the surface than the austenitic steels are.
The maximum voltage values oE the generator which have been mentioned previously show that passivated metallic materials make it possible to obtain maximum voltages ~hich are only slightly different from those which are obtained with non-passivated metallic materials. As a matter of fact, the relati-ve decrease between the extreme values obtained with rhodium or titanium is only about 20% and the values obtained with an elec-trolytic deposit of chromium on annealed copper or brass are substantially the same as the highest values obtained with a non-passivated metallic material.
It is surprising to note that the presence oE a passi-vating layer in accordance with the invention which contains ~13i775S9 inorganic compounds which are poor conductors of electrons ma-kes so little change in the maximum voltage values of the generator.
The invention also makes it possible to reduce the rate o~ circulation of the anodic suspension and therefore the feed and circulation pressures of the suspension. This results, on the one hand, in a saving with respect to the energy required for this purpose and, on the other hand, in a decrease in the stresses exerted on the surface of the cathode.
Furthermore, a collector in accordance with the inven-tion makes it possible to use an anodic suspension with a high concentration of active metallic particles. This results in an increase in the number o~ intermittent contacts between the said particles and the surace of the collector, without the risk o clogging the generator. This increase makes it possible to decrease the polarization of the cell in accordance with the invention for a given discharge intensity.
Of course, the invention is not limited to the embo-diment described above, on basis of which one can con-template other methods and forms of embodiment without thereby going beyond the scope of the invention.
Thus, the invention extends, for instance, to generators whose anodic suspension recirculation systems comprise eed devices of metals which are more electronegative than the anodic active materials.
It also covers, by way of example, embodiments in which the collector is permeable to the electrolyte and to the ions, in particular when it is made with a perforated plate or a grid which is separated from the cathode compartment or applied against the cathode compartment, a membrane permeable to the electrolyte and to the ions and impermeable to the particles being possibly disposed between the said plate or grid and the ~ 75S~
cathode compartment. It is furthermore obvious that the invention applies whatever the arrangement of the cells, in series or in parallel.
The invention is particularly concerned with such gene-rators in which the active material of the anode compartment, at times referred to as the fuel, is a metallic material.
When such a generator delivers electric current into a discharge circuit, the said active metallic material under-goes electrochemical oxidation in the anode compartment, losingelectron$, while the active material of the cathode compartment is reduced by the electrons coming from the anode compartmen-t via the intermediate discharge circuit.
It is already known to use the said active metallic material in the form oE a suspension of particles in an electro-lyte. The said active metallic particles then lose electrons in contact with an electrically conductive electron collector in the anode compartment, in particular a metallic electron collec-tor. However, when the said active metallic particles are in permanent contact with the electron collector, products result-ing from their oxidation accumulate frequently on or near their sur~aces. This ~esults in a passivating o~ the said active metallic particles, which makes their complete oxidation impos-sible.
It has been attempted to avoid this drawback by circu-lating the said suspension of active metallic particles in the anode compartment in such a manner that the active metallic par-ticles are in intermittent contact with the said electron collec-tor.By alternately feeding the active metallic particles into contact with the electron collector and removing them from same, the diffusing of the oxidation products-throughout the electro-lyte is favored.
. ' '. . , ' .
~L07~75S9 The passivation is furthermore retarded by circulating said suspension of active metallic particles outside of the anode compartment and recycling it into said anode compartment so that the active metallic particles again participate in the discharge reaction.
Actual practice shows that such generators can give acceptable results for experimental cells. On the other hand, in cells suitable for industrial applications, for instance for the driving of vehicles, namely in cells capable of provid-ing a ï ela-ti-~el~ large amount of power, active metallic parti-cles attach themselves to the surface of the electron collector when the latter is metallic, whatever the means used to move or recycle the suspension. These particles which are attached to the surface oE the electron collector cause an agglomerating of the other particles in suspension in the electrolyte. This agglomeration is propagated in the anode compartment. It may lead to obstruction of said compartment and considerably reduce the power of the cell as a result of the passivating of the agglomerated particles. This agglomeration can take place even when the suspension is circulated without the cell delivering current.
The properties o the elements forming the electro-chemical generator of the type to which the invention applies which affect the attaching and the agglomerating of the said particles seem to be very diversified and concern only the com-ponents of the anode compartment, in particular: physical pro-perties and constants of the material forming the surface of the collector; chemical and electrochemical behavior of the collector and of the active metallic particles and electrolyte;
liberation of gases.
The object of the present invention is to provide a collector and therefore a generator which are free of the ~77~59 above-indicated drawbacks.
Accordingly, the invention as herein broadly claimed is an electrochemical generator formed of at least one cell comprising, on the one hand, at least one anode compartment containing a suspension of active particles, formed at least in part of zinc, in an aqueous alkaline electrolyte and having an electron collector, the suspension circulating through the anode compartment in such a manner that the particles undergo intermittent and repeated contacts with the electron collector, and, on the other hand, at least one cathode compartment having a cathode with an active material, and characterized by the fact that the surface of the electron collector facing the suspension is make of a metallic material which is covered by a passivating layer, the layer containing at least one inorganic compound of at least one metal constituting at least in part the metallic material, the metal being selected from the group consisting of magnesium, scanaium, yttrium, lanthanum, titanium, zirconium, hafnium, niobium, tantalum and chromium.
This passivating layer, which is formed, for instance, when the electron collector is in contact with atmospheric air or the electrolyte, is indestructible by -the electrolyte and the anodic.suspension. This layer prevents direct contact of the anodic metallic particles with the metal material of the surface of the collector. The said inorganic compounds may, for instance, be salts, oxides, or hydroxides.
The metallic materials which can give rise to such passivation phenomena are, in particular, magnesium, metals of Groups IIIB, IVB, VB and VIB of the periodic classification of elements (Handbook of Chemistry and Physics, 53rd Edition, 1972-1973, published by the Chemical Rubber Co., of Cleveland, Ohio) and, more particularly, scandium, yttrium, lanthanum, titanium, zirconium, hafnium, niobium, tantalum, and chromium, ~ :~C377559 .:
or some of their alloys with each other or with other metals.
By active metallic particles of the anode compartment, there are understood particles formed in whole or in ~t - 3a -... . ..
~q37~5~9 active anodic material, for instance, particles the electroche-mically inactive center of which is covered with a shell formed of the active anodic material.
In accordance with preferred features of the invention:
a) the metallic material of the surface of the collec-tor consists of chromium or titanium;
b) the chromium is deposited electrolytically on an electron-conducting support, for instance a support of metal, or, when it is desired to produce collectors which are particularly light and/or of complicated shape, of a plastic material which has been made a conductor of electrons throughout or as a result of a coating;
c) -the anodic metallic particles are particl.es of zinc, d) the electrolyte .is an alkaline electrolyte, e) the active material o the cathode is oxygen or a compound of oxygen, for instance a metallic oxide, f) the anodic suspension is arranged in the cell between the cathode compartment and the anodic electron collector, g) a hydrophilic separator which is a non-conductor of electrons, is permeable to the electrolyte and to -the ions, and .is impermeable to the anodic particles is arranged between the anode compartment and the cathode compartment in orcler to prevent said particles from coming into contact with the electron-conduc-tive zones of the cathode, which would cause short circuits, h) the cell comprises a means for feeding and a means for discharging the said suspension, a means for the recycling and/or regenerating of the said suspension being possibly arranged between the discharge means and the feed means.
The invention will easily be understood from l:he follow-0 ing non-limitative example:
A zinc/air generator of a power of abo~t 50 watts, a diagrammatic cross sec-tion of which is shown in the accompanying ~L~'77559 drawing, is formed of a cell (1~. This cell (1) comprises a positive terminal and a negative terminal (which are not shown) connected by an electric discharge circuit (not shown). The essential elements of this cell (1) are arranged in the follow-ing manner:
In the cathode compartment (2) there can be observed the cathode, which is an air-diffusion electrode (21), the ca-thode active material being oxygen (flow of air not shown). This cathode (21) is formed, in known manner, essentially of carbon, silver, polytetrafluorethylene and nickel. This electrode (21) is covered on its surface (211) by a hydrophilic separator (3) which is a non-conductor of electrons, is permeable to ions and to the elec-trolyte, and is impermeable to the particles oE
æinc (~1). Facing the separator (3) there is arranged an anodic electron collector (42), which is a conductor of electrons, and is impermeable to the electrolyte, the ions and the zinc parti-cles.
The space between the surface (421) of the anodic elec-tron collector (42) and the separator (3) constitutes the anode compartment (4).
The cell (1) comprises at one end (5) a device (not shown) ~or the feeding of a suspension of zinc particles (41) in an electrolyte and at the other end (6) a device ( not shown) for discharging said suspension.
A device (7) makes it possible to circulate the suspen-sion in the anode compartment (4) and recycle it into said anode compartment via a system (8) which is external to the anode compartment. This external system comprises a feed device (81) which makes it possible to maintain the percentage by weight of zinc in suspension in the electrolyte constant, and a buffer reservoir (82~ of sui-table volume.
The particles (41) circulating in the anode compar-tment .
undergo intermittent and repeated contacts with the surface (421) of the anodic electron collector (42) during their passage through the cell.
The electrolyte consists of 6N potassium hydroxide ( 6 mols of KOH per liter) and the average diameter of the zinc particles (41) is 10-20 microns.
Such a cell ~1) serves for the carrying out of compara-tive operating tests with anodic electron collectors (42) whose surface (421) facing the suspension is made with different metals or alloys.
During each test, on the one hand, the intensity of the discharge current of the cell (1) is maintained constant, or instance equal to 150 mA per cm2 oE active surface (211) of the air electrode, and, on the other hand, the percentage by weight of zinc particles (41) in suspension in the electrolyte is maintained at a constant value of between 10% and 30% of the weight of the electrolyte. Furthermore, the circulating of the suspension in the cell ( 1) is effected with constant speeds of between 15 m/min and 30 m/min.
During the operation of the generator, the temperature of the electrolyte and of the anodic electron collector (42) remains substantially equal to ambient temperature (about 25C).
At the beginning of each test, the concentration of zinc dissolved in the form of potassium zincate in the electro-lyte is zero.It increases gradually during the discharge and when it reaches about 120 g/liter, beyond which value the particles of the anode suspension become practically inactive, the zincated electrolyte of the anode compartment ~4~ and of the system (8) is replaced by a fresh 6N potassium hydroxide solution free of potassium zincate and the test is contlnued by proceeding with a new discharge.
The metals or alloys used to produce the suriace (421) 6 ~ r ~L~7755~
of the electron collector ~42) belong to the following three groups:
A. Copper, nickel, iron, leadl used in the form of metal sheets;
~ cadmium used in the form of electrolytic deposit on a nickel sheet support;
- platinum, rhodium, gold, silver, used in the form of electrolytic deposits on a copper sheet support.
B. Titanium used in the form of a metal sheet;
- chromium used in theIform of electrolytic deposits on copper and brass sheet supports.
C. Stainless steel corresponding to the designation AFNOR Z6CNl~-09 tabout 0.07~ carbon, 17~ to 19~ chrom:ium, 8~ to 10~ nickel);
- stainless steel corresponding to the designation AFNOR Zl NCDU 25-20-4-2- ( at most 0.02~ carbon, a~ou-t 24~ to 27% nickel, 19~ to 22% chromium, less than 2% manganese, 4% to 4.8% molybdenum, 1% to 2% copper);
-stainless steel type ORION 26.1 oE the Societe Creu-sot-Loire (abou-t 0.002~ carbon, 26% chromium, 1~ molybdenum);
these three steels being used in the form of sheets.
The supports on which the electrolytic deposits are effected (groups A and B) are used in non-annealed and in an-nealed condition.
Experiment shows that the maximum voltages of the ge-nerator are obtained at the start of the tests, when the concen-tration o~ zinc dissolved in -the electrolyte in the form of po-tassium zincate is low.
Furthermore, the highest maximum voltages are produced when the rate of circulation is the lowest and the concentration of zinc particles the highes-t.
For a ra-te of circulation of 15 m/min, a current of ~7~55~ ~ !
150 mA per cm of active surface (211) of the air electrode and a concentration of zinc particles of 30~, the maximum ~oltages expressed in volts of the generator are substantially as follows, as a function of the different metallic materials used for the surface (421) of the collector (42):
A. Copper: 1.06 V; cadmium: 1.06V; nickel: 1.04V; iron:
0.95V; platinum: 1.06V; rhodium: 1.07V; gold: 1.03V; silver:
1.00V; lead: 0.98V;
B. Chromium on copper or brass, not annealed: 00875V;
chromium on copper or brass, annealed: 1.05V; titanium: 0.85V;
C. Stainless steel Z 6CN 18-09: 0.915V; stainless steel Z 1 NCDU 25-20-4-2: 0.91V; stainless steel ORION 26.1: 0 750V.
With respect to the attachment o~ the zinc part:icles to the surface (~21) of the collector (~2) and their aggLomera-tion, the following has been noted:
When the surface (421) of the collector (42) is made of one of the metals of group A or of the stainless steels Z 6 CN 18-09 and ORION 26.1 of group C, zinc particles attach themselves to the surface (421) of the collector (42) and form agglomerates. This takes place before the end of the first discharge has been reached, that is to say before the concentra-tion oE zinc dissolved in the electrolyte reaches the maximum permitted value of 120 g/liter. If the test is contlnued, the anode compartment (4) gradually becomes clogged. Circulation of the suspension of particles becomes impossible, whatever the device used to effect the circulation. At the same time, the voltage of the generator decreases rapidly and becomes practi-cally zero as a result of the accelerated passivation of the agglomerated particles. The generator thus becomes unusable upon the first discharge, whatever the weight of zinc in suspension in the electrolyte, the rate of circulation of the suspension, and the intensity of the discharge current.
~77559 When the surface (421) of the collector (42) is made of one of the metals of group B or of stainless steel ~ l NCDU
25-20-4-2 of group C, no attachment of the anodic particles to the collector takes place and no agglomeration, whatever the weight of zinc in suspension in the electrolyte, the rate of circulation of the suspension, and the intensity of the dischar-ge current.
If it happens that particles should momentarily become immobilized at the collector, they are again placed in circula-tion shortly afterwards without forming agglomerates. Moreover, the uniform decrease of the voltage of the generator caused by the increase in the zincate content of the electrolyl;e is rela-tively small, of the order of 10~ as compared with the maximum voltage at the start of discharge for an intensity of the discharge current equal to 150mA per cm2 of active surface of the air electrode. It is sufficient to renew the 6N potassium hydroxide solution when its concentration of dissolved zinc reaches the limit value predetermined for effecting repeated discharges.
As a matter of fact, the operation of the generator i5 limited only by the life of the air electrode. This life may easily exceed several hundred discharges. The same result can be obtained if, instead of renewing the electrolyte when its concentration reaches a predetermined limit value, a con~inuous regeneration of the electrolyte is effected in an attached de-vice.
Metals of group A are not is passivated sta-te under the conditions of the test. Metals of groups B, that is to say chromium and titanium, are on the other hand passivated in con-tact with the air or the electrolyte under the condit:Lons of the experiment, their surface becoming covered with a layer formed primarily of higher or lower hydrates of oxides of these metals.
g _ 1~77559 This test, therefore, shows -that the presence of this passivating layer avoids the attachment and agglomeration of the zinc particles on the surface of the collector. This pheno-menon apparently could be attributed to a modification of the electrochemical behavior of the combination formed by the surface of the metallic collector, the electrolyte, and the anodic sus-pension. Likewise, the difference in the results obtained with the three types of stainless steels (group C , all of which con-tain chromium in an amount theoretically suf icient to obtain on the surface of the collector a passivating film of higher or lower hydrates of chromium oxides can apparently be attributed to the following facts. On the one hand, the austenitic steel Z 6 CN-18-09, contrar~ to austenitic steel ~1 NCDU 25-20-~-2, i5 thermodynamically unstable a-t the low temperatures of use of the generator, these temperatures being generally between 20C.
and 60C., and its percentage of carbon is relatively high, which two factors may result in a break in passivity of the surface.
On the other hand, steel ORION 26.1, since it is ferritic, is more sensitive to the break in passivity of the surface than the austenitic steels are.
The maximum voltage values oE the generator which have been mentioned previously show that passivated metallic materials make it possible to obtain maximum voltages ~hich are only slightly different from those which are obtained with non-passivated metallic materials. As a matter of fact, the relati-ve decrease between the extreme values obtained with rhodium or titanium is only about 20% and the values obtained with an elec-trolytic deposit of chromium on annealed copper or brass are substantially the same as the highest values obtained with a non-passivated metallic material.
It is surprising to note that the presence oE a passi-vating layer in accordance with the invention which contains ~13i775S9 inorganic compounds which are poor conductors of electrons ma-kes so little change in the maximum voltage values of the generator.
The invention also makes it possible to reduce the rate o~ circulation of the anodic suspension and therefore the feed and circulation pressures of the suspension. This results, on the one hand, in a saving with respect to the energy required for this purpose and, on the other hand, in a decrease in the stresses exerted on the surface of the cathode.
Furthermore, a collector in accordance with the inven-tion makes it possible to use an anodic suspension with a high concentration of active metallic particles. This results in an increase in the number o~ intermittent contacts between the said particles and the surace of the collector, without the risk o clogging the generator. This increase makes it possible to decrease the polarization of the cell in accordance with the invention for a given discharge intensity.
Of course, the invention is not limited to the embo-diment described above, on basis of which one can con-template other methods and forms of embodiment without thereby going beyond the scope of the invention.
Thus, the invention extends, for instance, to generators whose anodic suspension recirculation systems comprise eed devices of metals which are more electronegative than the anodic active materials.
It also covers, by way of example, embodiments in which the collector is permeable to the electrolyte and to the ions, in particular when it is made with a perforated plate or a grid which is separated from the cathode compartment or applied against the cathode compartment, a membrane permeable to the electrolyte and to the ions and impermeable to the particles being possibly disposed between the said plate or grid and the ~ 75S~
cathode compartment. It is furthermore obvious that the invention applies whatever the arrangement of the cells, in series or in parallel.
Claims (13)
1. An electrochemical generator formed of at least one cell comprising, on the one hand, at least one anode compartment containing a suspension of active particles, formed at least in part of zinc, in an aqueous alkaline electrolyte and having an electron collector, the suspension circulating through the anode compartment in such a manner that the particles undergo intermit-tent and repeated contacts with the electron collector, and, on the other hand, at least one cathode compartment having a cathode with an active material, and characterized by the fact that the surface of the electron collector facing the suspension is made of a metallic material which is covered by a passivating layer, the layer containing at least one inorganic compound of at least one metal constituting at least in part the metallic material, the metal being selected from the group consisting of magnesium, scandium, yttrium, lanthanum, titanium, zirconium, hafnium, niobium, tantalum and chromium.
2. The electrochemical generator according to claim 1, characterized by the fact that the said metallic material is chromium.
3. The electrochemical generator according to claim 1, characterized by the fact that the said metallic material is titanium.
4. The electrochemical generator according to claim 1, characterized by the fact that the said metallic material is an austenitic stainless steel containing iron, nickel, and chromium, said steel being thermodynamically stable at the temperature of use of the generator and containing at most 0.02% carbon.
5. The electrochemical generator according to claim 2, characterized by the fact that the said chromium surface is made by electrolytic chrome-plating on a support which is a conductor of electrons.
6. The electrochemical generator according to claim 5, characterized by the fact that the said electron collector sup-port is a metallic material.
7. The electrochemical generator according to claim 6, characterized by the fact that the said support of metallic material is annealed.
8. The electrochemical generator according to claim 1, characterized by the fact that the active material of the cathode is oxygen or a compound of oxygen.
9. The electrochemical generator according to claim 1, characterized by the fact that the suspension of active metallic particles is arranged between the electron collector and the cathode compartment.
10. The electrochemical generator according to claim 9, characterized by the fact that the said electron collector is impermeable to the electrolyte, to ions, and to the active metallic particles.
11. The electrochemical generator according to claim 1, characterized by the fact that the anode compartment and the cathode compartment are separated by means of a hydrophilic separator which is a non-conductor of electrons, is permeable to the electrolyte and to ions, and is impermeable to the active metallic particles.
12. The electrochemical generator according to claim 1, characterized by the fact that the cell comprises a means for the feeding of said suspension and a means for the discharging of said suspension.
13. The electrochemical generator according to claim 12, characterized by the fact that the discharge means is connected to the feed means by a recycling means.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7524205A FR2319982A1 (en) | 1975-08-01 | 1975-08-01 | ELECTROCHEMICAL GENERATOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1077559A true CA1077559A (en) | 1980-05-13 |
Family
ID=9158702
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA257,750A Expired CA1077559A (en) | 1975-08-01 | 1976-07-26 | Electrochemical generator with passivated electron collector |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5219232A (en) |
| AU (1) | AU499989B2 (en) |
| CA (1) | CA1077559A (en) |
| DE (1) | DE2632152C3 (en) |
| FR (1) | FR2319982A1 (en) |
| GB (1) | GB1547487A (en) |
| IT (1) | IT1069530B (en) |
| NL (1) | NL166364C (en) |
| SE (1) | SE413446B (en) |
| SU (1) | SU673207A3 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS52110441A (en) * | 1976-03-13 | 1977-09-16 | Kogyo Gijutsuin | Zinc alkali storage battery |
| JPS59143205U (en) * | 1983-03-15 | 1984-09-25 | リンナイ株式会社 | gas stove trivet |
| NL8800500A (en) * | 1988-02-26 | 1989-09-18 | Stork Screens Bv | ELECTRODE MATERIAL FOR APPLICATION IN A SUSPENSION ACCUMULATOR SEMI-CELL, ACCUMULATOR SEMI-CELL WITH AN ELECTRODE OF SUCH MATERIAL AND SUCH ACCUMULATOR SEMI-CELL CONTAINING BATTERY. |
| JP6290509B2 (en) * | 2014-08-29 | 2018-03-07 | シャープ株式会社 | Air electrode battery using zinc slurry negative electrode with carbon additive |
| CN111003794B (en) * | 2019-12-25 | 2022-10-04 | 广州市环境保护工程设计院有限公司 | Artificial wetland system for treating rural domestic sewage |
-
1975
- 1975-08-01 FR FR7524205A patent/FR2319982A1/en active Granted
-
1976
- 1976-07-16 DE DE2632152A patent/DE2632152C3/en not_active Expired
- 1976-07-23 SU SU762381099A patent/SU673207A3/en active
- 1976-07-26 CA CA257,750A patent/CA1077559A/en not_active Expired
- 1976-07-30 GB GB31931/76A patent/GB1547487A/en not_active Expired
- 1976-07-30 IT IT68917/76A patent/IT1069530B/en active
- 1976-07-30 NL NL7608498.A patent/NL166364C/en active
- 1976-07-30 SE SE7608630A patent/SE413446B/en unknown
- 1976-08-02 JP JP51092272A patent/JPS5219232A/en active Granted
- 1976-08-02 AU AU16466/76A patent/AU499989B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2319982A1 (en) | 1977-02-25 |
| SE413446B (en) | 1980-05-27 |
| FR2319982B1 (en) | 1980-09-19 |
| SU673207A3 (en) | 1979-07-05 |
| GB1547487A (en) | 1979-06-20 |
| DE2632152C3 (en) | 1980-07-17 |
| JPS5754911B2 (en) | 1982-11-20 |
| AU1646676A (en) | 1978-02-09 |
| IT1069530B (en) | 1985-03-25 |
| SE7608630L (en) | 1977-02-02 |
| AU499989B2 (en) | 1979-05-10 |
| DE2632152A1 (en) | 1977-02-03 |
| JPS5219232A (en) | 1977-02-14 |
| DE2632152B2 (en) | 1979-11-08 |
| NL7608498A (en) | 1977-02-03 |
| NL166364C (en) | 1981-07-15 |
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