CA1132097A - Electrolyte cell membrane of polyantimonic acid and organic binder - Google Patents
Electrolyte cell membrane of polyantimonic acid and organic binderInfo
- Publication number
- CA1132097A CA1132097A CA294,851A CA294851A CA1132097A CA 1132097 A CA1132097 A CA 1132097A CA 294851 A CA294851 A CA 294851A CA 1132097 A CA1132097 A CA 1132097A
- Authority
- CA
- Canada
- Prior art keywords
- membrane
- anode
- cathode
- weight percent
- binding agent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B13/00—Diaphragms; Spacing elements
- C25B13/04—Diaphragms; Spacing elements characterised by the material
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/70—Assemblies comprising two or more cells
- C25B9/73—Assemblies comprising two or more cells of the filter-press type
-
- 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
- H01M8/02—Details
- H01M8/0289—Means for holding the electrolyte
-
- 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
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
-
- 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
Abstract
ABSTRACT OF THE DISCLOSURE
A membrane for an electrochemical cell, inhibiting the diffusion of gases and allowing ionic conduction. The mem-brane comprises from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of polyantimonic acid powder, the grain size of the polyantimonic acid powder being less than 38 µm. The membrane is selectively permeable to cations in a basic medium and is selectively permeable to anions in an acidic medium. The membrane overcomes disadvantages of prior art membranes. An electrochemical cell comprising the membrane is also disclosed.
A membrane for an electrochemical cell, inhibiting the diffusion of gases and allowing ionic conduction. The mem-brane comprises from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of polyantimonic acid powder, the grain size of the polyantimonic acid powder being less than 38 µm. The membrane is selectively permeable to cations in a basic medium and is selectively permeable to anions in an acidic medium. The membrane overcomes disadvantages of prior art membranes. An electrochemical cell comprising the membrane is also disclosed.
Description
`~ ~13Z0~7 The present invention relates to a membrane, for an electrochemical cell, inhibiting gas diffusion but allowing ionic conduction.
More ~articularly, the present invention relates to a membrane consisting of an organic binding agent and an ion con-ducting inorganic powder, embedded in the binding agent in which the inorganic powder maintains its ionic conductivity.
Membranes of this type are known from, e.g., French patent No. 1,417,585 and Belgian patent No. 649,390. However, these known membranes are only found in units exclusively provi-ded for fuel cells and they comprise inorganic ionic conductors which are not stable in a basic medium.
Accordingly, an object of the present invention is to provide a membrane whic~ obviates or mitigates the above noted disadvantages of the prior art.
According to an aspect of the present invention there is provided a membrane for an electrochemical cell, inhibiting the diffusion of gases and allowing ionic conduction, comprising from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of polyanti-monic acid powder, the grain size of the polyantimonic acid powder being less than 38 ~m; the membrane being selectively permeable to cations in a basic medium and being selectively permeable to anions in an acidic medium.
According to a further aspec-t of the present invention there is provided an electrochemical cell comprising the above defined membrane.
The membrane disclosed herein is stable in a basic medium and it can be adapted for use in an electrolytic cell. It may, particularly but not exclusively, be used in an electrolytic ..
` 113Z097 cell for producing hydrogen.
The ionic conducting powder for the membrane disclosed herein is polyantimonic acid. The fact that polyantimonic acid, with the general formula {(H3Sb3O5(OH)8)3 (H5 5 6 18 ion exchanger is known, e.g., from L.H. Baetslé and D. Huys, J. Inorg. Nucl. Chem., 30r 639 to 649, (1968).
However, a membrane comprising polyantimonic acid as an ion conducting inorganic powder has a number of unexpected and advantageous properties: the high capacity of polyantimonic acid for exchanging cations is maintained in a membrane contain-ing an organic binding agent; such a membrane has a pronounced selectivity for ions; the resistivity of the membrane is low at normal operating temperatures, the more so, if the amount of organic binding agent is about 20~; the resistance of the mem-brane remains constant in terms of current density; the membrane keeps its physico-chemical and electrochemical properties up to a temperature of approximately 150C in a highly concentrated alkaline medium; the gas separating characteristic of the membrane is good; and the concentration of electrolyte with which the membrane is in contact is not critical for the conductivity of the membrane.
A membrane in association with an electrolytic cell for producing hydrogen is known, e.g., from the paper by L.J. Nuttall and W.A. Titterington - Conference on the Electrolytic Production of Hydrogen - City University London - February 25-26, 1975.
In this known cell, the membrane is made of sulphonated and polymerized tetrafluoroethene and it is located between one electrode, which acts as a catalyst, and functions as the anode of the cell and which is made of a special alloy, and a second electrode, which also acts as a catalyst, but functions as the
More ~articularly, the present invention relates to a membrane consisting of an organic binding agent and an ion con-ducting inorganic powder, embedded in the binding agent in which the inorganic powder maintains its ionic conductivity.
Membranes of this type are known from, e.g., French patent No. 1,417,585 and Belgian patent No. 649,390. However, these known membranes are only found in units exclusively provi-ded for fuel cells and they comprise inorganic ionic conductors which are not stable in a basic medium.
Accordingly, an object of the present invention is to provide a membrane whic~ obviates or mitigates the above noted disadvantages of the prior art.
According to an aspect of the present invention there is provided a membrane for an electrochemical cell, inhibiting the diffusion of gases and allowing ionic conduction, comprising from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of polyanti-monic acid powder, the grain size of the polyantimonic acid powder being less than 38 ~m; the membrane being selectively permeable to cations in a basic medium and being selectively permeable to anions in an acidic medium.
According to a further aspec-t of the present invention there is provided an electrochemical cell comprising the above defined membrane.
The membrane disclosed herein is stable in a basic medium and it can be adapted for use in an electrolytic cell. It may, particularly but not exclusively, be used in an electrolytic ..
` 113Z097 cell for producing hydrogen.
The ionic conducting powder for the membrane disclosed herein is polyantimonic acid. The fact that polyantimonic acid, with the general formula {(H3Sb3O5(OH)8)3 (H5 5 6 18 ion exchanger is known, e.g., from L.H. Baetslé and D. Huys, J. Inorg. Nucl. Chem., 30r 639 to 649, (1968).
However, a membrane comprising polyantimonic acid as an ion conducting inorganic powder has a number of unexpected and advantageous properties: the high capacity of polyantimonic acid for exchanging cations is maintained in a membrane contain-ing an organic binding agent; such a membrane has a pronounced selectivity for ions; the resistivity of the membrane is low at normal operating temperatures, the more so, if the amount of organic binding agent is about 20~; the resistance of the mem-brane remains constant in terms of current density; the membrane keeps its physico-chemical and electrochemical properties up to a temperature of approximately 150C in a highly concentrated alkaline medium; the gas separating characteristic of the membrane is good; and the concentration of electrolyte with which the membrane is in contact is not critical for the conductivity of the membrane.
A membrane in association with an electrolytic cell for producing hydrogen is known, e.g., from the paper by L.J. Nuttall and W.A. Titterington - Conference on the Electrolytic Production of Hydrogen - City University London - February 25-26, 1975.
In this known cell, the membrane is made of sulphonated and polymerized tetrafluoroethene and it is located between one electrode, which acts as a catalyst, and functions as the anode of the cell and which is made of a special alloy, and a second electrode, which also acts as a catalyst, but functions as the
- 2 -.~
' i~3;~097 cathode of the cell and is made of platinum black. This known unit is preferably utilized in an acid medium as a consequence of which the choice and price of the materials used are adversely affected. However, when the electrolytic cell is utilized in an alkaline medium, the membrane causes a significant drop in - potential, due to its comparatively high resistivity and thick-ness, the latter of which is necessary for inhibiting the dif-fusion of a gas.
The membrane described herein overcomes these drawbacks and has a less significant drop of potential than the above described membranes when the electrolytic cell is working.
Ion conducting membranes comprising an oxide of anti-mony are known, e.g., from U.S. patents No. 3,346,422 and No.
; 3,437,580. The membranes described herein differ from these known membranes, inter alia as follows:
On the one hand, the antimonyoxidesof the prior art membranes do not have a polymeric character, contrary to poly-antimonic acid used in the membranes described herein; polyanti-monic acid has a crystalline structure with a recur_ent "unitary cell". On the other hand, the above known membranes have a sintered structure of a compressed inorganic material, whereas the membranes described herein comprise both an organic binding agent and polyantimonic acid, the latter being an inorganic powder.
It follows that the membranes described herein are composed of a heterogeneous material consisting of two differen-t materials which are not sintered and can, for instance, be agglo-merated by dry rolling according to a preferred embodiment.
The characterlstics of the membranes described herein are basically different from those of known membranes comprising
' i~3;~097 cathode of the cell and is made of platinum black. This known unit is preferably utilized in an acid medium as a consequence of which the choice and price of the materials used are adversely affected. However, when the electrolytic cell is utilized in an alkaline medium, the membrane causes a significant drop in - potential, due to its comparatively high resistivity and thick-ness, the latter of which is necessary for inhibiting the dif-fusion of a gas.
The membrane described herein overcomes these drawbacks and has a less significant drop of potential than the above described membranes when the electrolytic cell is working.
Ion conducting membranes comprising an oxide of anti-mony are known, e.g., from U.S. patents No. 3,346,422 and No.
; 3,437,580. The membranes described herein differ from these known membranes, inter alia as follows:
On the one hand, the antimonyoxidesof the prior art membranes do not have a polymeric character, contrary to poly-antimonic acid used in the membranes described herein; polyanti-monic acid has a crystalline structure with a recur_ent "unitary cell". On the other hand, the above known membranes have a sintered structure of a compressed inorganic material, whereas the membranes described herein comprise both an organic binding agent and polyantimonic acid, the latter being an inorganic powder.
It follows that the membranes described herein are composed of a heterogeneous material consisting of two differen-t materials which are not sintered and can, for instance, be agglo-merated by dry rolling according to a preferred embodiment.
The characterlstics of the membranes described herein are basically different from those of known membranes comprising
- 3 -. .
. -- .
ll~Z097 antimony oxides. For example, the ion exchange properties, the resistivity and the resistance of the membranes described herein, during electrolysis, are significantly better relative to the prior art membranes. On the other hand, with membranes contain-ing Sb2O3xH2O undesirable secondary electrochemical reactions are ; possible in an electrolytic cell.
Preferably at least one surface of the membrane is coated with an electrode.
More preferably a surface oE the membrane is coated with an active electrode (anode) which acts as a catalyst and the other surface of the membrane is coated with an active elec-trode (cathode) which also acts as a catalyst.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
;~ Figure 1 is a schematic sectional view of an electroly-tic cell comprising a membrane as described herein; and Figure 2 is a larger-scale sectional view through a part of a unit of the electrolytic cell of Fig. 1.
The electrolytic cell of Fig. 1 and the unit of Fig. 2 comprise a membrane indicated by the reference number 5.
Composition Of The Membrane The membrane 5 is made of grains of polyantimonic acid which are ernbedded in an organic binding agent, preferably poly-tetrafluoroethene.
The polyantirnonic acid particles have, for instance, a maximum dimension of about 500 Angstr~m. However, many particles can coalesce to form a conglomerate which can have a maximum dimension of some tens of microns. This maximum dimension should, preferably, not be greater than 30 microns.
, ` il13Z0~7 The membrane, preferably, comprises a polymeric mate-rial as a binding agent. The polymeric material is, preferably, the aforesaid polytetrafluoroethene, although,as a rule, a hydro-philic polymer, for instance, polyethene can also be used.
The amount of binding agent relative to the amount of ion conducting powder should be sufficient to form a membrane.
If polytetrafluoroethene is used as the binding agent, the mini-mum amount relative to the complete membrane can be 2.5% by weight. A membrane containing at least 5% by weight of the binding agent is preferred. However, the amount of binding agent relative to the amount of polyantimonic acid powder must not be so high as to result in the powder loosing its ionic conductivity within the membrane. If polytetrafluoroethene is used as the binding agent, the maximum quantity relative to the complete membrane can be 30% by weight. A membrane comprising at the most 20% by weight of the binding agent is preferred.
Characteristics Of The Membrane . . ~
The membrane 5, particularly, as used herein manifests advantageous properties generally not available with prior art membranes.
a. Ion Exchange Characteristics Due to the amphoteric character of polyantimonic acid, the mem-brane is an anion exchanger in an acid medium and a cation exchanger in a basic medium. The active OH groups give H ions only in a basic medium; the exchange capacity for cations is a measure of the amount of active groups within the membrane which are capable of exchanging H ions for other cations such as K
and Na .
Table I shows that the exchange capacity, for cations, of poly-- ~0 antimonic powder is maintained after the powder has been bound -:
., : .
113Z0~7 with a binding agent (polytetrafluoroethene) to form a membrane.
TABLE I
Exchange capacity for cations at pH 7 expressed in milliequiva-lents per gram of polyantimonic acid.
..~
Exchange Capacity For Cations (meq.g 1) Powder Membrane _ NaOH 2.8 2.3 KOH 2.0 1.8 b. Selectivity For Ions Apart from its high cation exchange capacity, the membrane has a pronounced selectivity for ions.
This selectivity for ions is characterized by the transport numbers for cations and anions, t+ and t , respectively.
The transport number ti represents the fraction of the charge transported through the membrane by the i-ions. A dynamic measurement of the selectivity at 30C for the polyantimonic acid membrane gives a transport number tK+ amounting to 0.75.
c. Resistivity :
In Te_ms Of Temperature Table II shows the resistance of the membrane in terms of tempe-rature for a lN NaOH and a lN KOH electrolyte. The values were measured by means of a Hewlett-Packard AC bridge at 1,000 Hz.
TABLE II
Resistance of the membrane as a function of temperature at 1,000 Hz 2 Temperature Resistance of M~ mbrane (Qcm ) C lN NaOH lN KOH
1.25 1.75 3 50 0.91 1.16 : __ . __ . . _ . __.
',:
; ' ' , :
1~3Z097 The values of Table II relate to a membrane consisting of 80 weight percent polyantimonic acid and 20 weight percent polyte-trafluoroethene.
In Terms Of Amount Of Binding Agent Table III shows the resistivity of the membrane in terms of the amount of binding agent (polytetrafluoroethene) contained there-in. The values were measured by means ofa 1,000 Hz AC bridge at room temperature in a 25 weight percent KOH solution.
TABLE III
Resistivity as a function of the amount of binding agent.
Weight of Resistivity Binding Agent (Qcm) (~) ` 20 280 ' 20 25 ~,.
d. Resistance During Electrolysis Table IV shows -the resistance of the membrane as a function of temperature; this resistance is a measure of the drop in potent-~tial through the membrane.
,~ 30 , ,' `
( ' '`.~
TABLE IV
T ( C~ R (Qcm ) 5.8xlO-83 2.8xlO-105 2.5xlO-l Since the resistance of the membrane remains constant as a function of current density, it is possible, for instance, to allow an electrolytic cell to work at 10 to 15 kAm 2 at tempera-tures higher than 100C with a drop in potential through the membrane that is only 0.15 V to 0.25 V.
e. Stability The membrane maintains its physico-chemical and electrochemical characteristics up to 150C in a highly concentrated alkaline medium, contrary to the organic ion exchange membranes in current use.
f. Gas Separating Character From the volume of the pores and the distribution thereof, as determined by means of the N2-adsorption isotherm (BET method), it was determined that, for the polyantimonic acid powder used in the tests, the grains were free from internal porosity and had a diameter less than 500 Angstr~m. However, these grains form conglomerates which may have diameters of tens of microns. If such macro-grains, the diameter of which ranges from 212 ~m to 38~m, are used as a starting material and they are mixed with polytetrafluoroethene in a ratio of 80/20, 18~ of H2 will be found in the oxygen gas flow during the electrolysis of water at atmospheric pressure. If, however, grains with a dimension smaller than 38 ~m are used as the startins material, 1 to 2% of H2 will be found in -the oxygen gas flow, the working conditions . ~
~13Z097 being the same. For the membrane to act as a gas separator, the size of the macro-grains must not exceed a certain upper limit.
Use Of The Membrane In An Electrolytic Cell The details given below are for the electrolysis of water which is dissociated into hydrogen and oxygen, but the application of the membrane is not limited to this use.
The electrolytic cell shown in Fig. 1 comprises a con-tainer 1 which is divided into chambers 2 and 3 by a unit. This unit comprises an electrode 4 acting as a cathode, the membrane 5, described above, and an electrode 6 acting as an anode. The electrodes 4 and 6 are connected to a potential source 9 by the conductors 7 and 8, respectively, which pass through the wall of the container 1.
The chambers 2 and 3, which are filled with electro-lyte, each form a part of two liquid circuits (no* shown). The products resulting from the electrolysis are recovered in those circuits outside the chambers 2 and 3.
ln chamber 2 the liquid flows from the inlet 10 to the outlet 11. Outside the chamber, the outlet 11 is connected to the inlet 10 through a pipe system, a pump and apparatus for re-covering the products developed by the electrolysis; the pipe system, pump and recovery apparatus are not shown.
In chamber 3 the liquid flows from the inlet 12 to the outlet 13. Outside the chamber, the outlet 13 is connected to the inlet 12 through a pipe system, a pump and apparatus for recovering the products developed by the electrolysis; the pipe system, pump and recovery apparatus are not shown.
If -the liquid is alkaline, the electrochemical re-actions are as follows, according to -the generally accepted g '~
1~3Z097 theory:
at the cathode : 4 H2O + 4 e ~ 4 OH + 2 H2 at the anode 2 2 thus, the resultant reaction is ; 2 H2O ~ 2 H2 + 2 The electrons (e ) are transported through the potent-ial source 9 from the anode 6 towards the cathode 4. The elec-tric circuit is closed by ionic conduction through the membrane 5.
Thus, the mernbrane 5 ensures ionic conduction from one electrode to the other; furthermore, the membrane also separates the gases resulting from the electrolysis.
The ionic conduction takes place by cations and/or anions, depending on the capacity of the membrane for exchanging either anions or cations. The selectivity of the membrane for ions determines whether the majority of the current is transport-ed in the membrane by the cations or anions. Thus, with poly-antimonic acid in a KOH medium, it is mainly the K ions that will migrate from the anode 6 towards the cathode 4, whilst in a NaOH medium it is mainly the Na ions which migrate.
In order to ensure the separation of gases, the mem-brane has a finite thic~ness depending on its composition and on the type and amount of binding agent it contains. The optimum thickness of a membrane comprising 20% by weight of polytetra-; fluoroethene, as a binding agent, is, for instance, 200 microns.
` The electrodes 4 and 6 between which the membrane is - located in close contact therewith to form a unit can be prepared` in a number of different ways.
In the unit shown in Fig. 2, the electrode acting as the cathode is made from a gauze 15 and an electrically conduct-ing coating 14 which acts as a catalyst and covers the gauze 15.
-- ~.`' :~32097 The electrode acting as the anode is made from a gauze 17 and an electrically conducting coating 16 which acts as a catalyst and covers the gauze 17. The gauzes 15 and 17 act as conducting collectors for the input and output of current. The unit was prepared as follows:
A 55 mesh nickel wire gauze with a wire thickness of 3701lmand an area of 100 cm2 was used for the collector 15.
Electrolytic platinum was deposited on this gauze, to form the coating 14, using a solution containing 3% by weight of H2PtC16 ; 10 salt. The electrolytic deposition was carried out at room tempe-rature, the current density being kept at 2 kAm 2 for 30 minutes.
In this way, there was formed on the nickel gauze 15 a porous coating of platinum, active as a catalyst, of about 1.5 mg per cm .
The coating 16 was prepared by mixing nickel nitrate and cobalt nitrate in l-butanol and at a stoichiometric ratio in order to obtain NiCo2O4. The collector 17 was made from the same nickel wire gause as was used for collector 15. This gauze was dipped into the NiCo2O4 solution, after which it was dried for 2 or 3 minutes at 250 C in an oven. This operation was repeated ten times and the electrode was finally heated at 350C
and kept for about 10 hours at that temperature. In this way, a coating of NiCo2O4, active as a catalyst, was deposited on the porous nickel. In the unit, the nickel gauzes 15 and 17 will ` ensure the transport of the electrons.
The preparation of the coating 16 was similar to the preparation of mixed oxides for oxygen-evolution-electrodes des-cribed by G. Sing, M.H. Miles and S. Srinivasan, BNL - 20,984 (1975)-- 30 For preparing the membrane 5, 4 g of polyantimonic acid .
powder with a yrain size less than 30 microns and a specific area (BET) of 25 m /g, available under the trade mark POLYAN from Applied Research, 1,080 Brussels, and 1 g of polytetrafluoro-ethene (Du Pont type 6N) were mixed together. ~The preparatiOn - of polyantimonic acid is known, e.g., from Belgian patent No.
649,746). This mixture was agglomerated by rolling to a thick-ness of 300 llm, by about ten passages through a rolling-mill.
The membrane 5 thus formed was placed on top of the gauze 15, precoated with the active catalyst coating 14. The gauze 17 precoated with the active catalyst coating 16 was then placed on top of the membrane 5; and these three layers were formed into a unit of 800 ~m thickness by rolling.
The unit thus prepared was immersed in 6N KOH. By connecting the gauze 15 and the gauze 17 to an external potential source, the fol]owing results were achieved.
The total potential drop (E) through the unit, expres-sed in volts, was measured for current strengths expressed in kilo-ampere per square meter for temperatures of 22C, 50C and 20I (kA/~I )E 22 C (V) E 50 C (V) E 85 C (V) 2 1.61 1.55 1.47
. -- .
ll~Z097 antimony oxides. For example, the ion exchange properties, the resistivity and the resistance of the membranes described herein, during electrolysis, are significantly better relative to the prior art membranes. On the other hand, with membranes contain-ing Sb2O3xH2O undesirable secondary electrochemical reactions are ; possible in an electrolytic cell.
Preferably at least one surface of the membrane is coated with an electrode.
More preferably a surface oE the membrane is coated with an active electrode (anode) which acts as a catalyst and the other surface of the membrane is coated with an active elec-trode (cathode) which also acts as a catalyst.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
;~ Figure 1 is a schematic sectional view of an electroly-tic cell comprising a membrane as described herein; and Figure 2 is a larger-scale sectional view through a part of a unit of the electrolytic cell of Fig. 1.
The electrolytic cell of Fig. 1 and the unit of Fig. 2 comprise a membrane indicated by the reference number 5.
Composition Of The Membrane The membrane 5 is made of grains of polyantimonic acid which are ernbedded in an organic binding agent, preferably poly-tetrafluoroethene.
The polyantirnonic acid particles have, for instance, a maximum dimension of about 500 Angstr~m. However, many particles can coalesce to form a conglomerate which can have a maximum dimension of some tens of microns. This maximum dimension should, preferably, not be greater than 30 microns.
, ` il13Z0~7 The membrane, preferably, comprises a polymeric mate-rial as a binding agent. The polymeric material is, preferably, the aforesaid polytetrafluoroethene, although,as a rule, a hydro-philic polymer, for instance, polyethene can also be used.
The amount of binding agent relative to the amount of ion conducting powder should be sufficient to form a membrane.
If polytetrafluoroethene is used as the binding agent, the mini-mum amount relative to the complete membrane can be 2.5% by weight. A membrane containing at least 5% by weight of the binding agent is preferred. However, the amount of binding agent relative to the amount of polyantimonic acid powder must not be so high as to result in the powder loosing its ionic conductivity within the membrane. If polytetrafluoroethene is used as the binding agent, the maximum quantity relative to the complete membrane can be 30% by weight. A membrane comprising at the most 20% by weight of the binding agent is preferred.
Characteristics Of The Membrane . . ~
The membrane 5, particularly, as used herein manifests advantageous properties generally not available with prior art membranes.
a. Ion Exchange Characteristics Due to the amphoteric character of polyantimonic acid, the mem-brane is an anion exchanger in an acid medium and a cation exchanger in a basic medium. The active OH groups give H ions only in a basic medium; the exchange capacity for cations is a measure of the amount of active groups within the membrane which are capable of exchanging H ions for other cations such as K
and Na .
Table I shows that the exchange capacity, for cations, of poly-- ~0 antimonic powder is maintained after the powder has been bound -:
., : .
113Z0~7 with a binding agent (polytetrafluoroethene) to form a membrane.
TABLE I
Exchange capacity for cations at pH 7 expressed in milliequiva-lents per gram of polyantimonic acid.
..~
Exchange Capacity For Cations (meq.g 1) Powder Membrane _ NaOH 2.8 2.3 KOH 2.0 1.8 b. Selectivity For Ions Apart from its high cation exchange capacity, the membrane has a pronounced selectivity for ions.
This selectivity for ions is characterized by the transport numbers for cations and anions, t+ and t , respectively.
The transport number ti represents the fraction of the charge transported through the membrane by the i-ions. A dynamic measurement of the selectivity at 30C for the polyantimonic acid membrane gives a transport number tK+ amounting to 0.75.
c. Resistivity :
In Te_ms Of Temperature Table II shows the resistance of the membrane in terms of tempe-rature for a lN NaOH and a lN KOH electrolyte. The values were measured by means of a Hewlett-Packard AC bridge at 1,000 Hz.
TABLE II
Resistance of the membrane as a function of temperature at 1,000 Hz 2 Temperature Resistance of M~ mbrane (Qcm ) C lN NaOH lN KOH
1.25 1.75 3 50 0.91 1.16 : __ . __ . . _ . __.
',:
; ' ' , :
1~3Z097 The values of Table II relate to a membrane consisting of 80 weight percent polyantimonic acid and 20 weight percent polyte-trafluoroethene.
In Terms Of Amount Of Binding Agent Table III shows the resistivity of the membrane in terms of the amount of binding agent (polytetrafluoroethene) contained there-in. The values were measured by means ofa 1,000 Hz AC bridge at room temperature in a 25 weight percent KOH solution.
TABLE III
Resistivity as a function of the amount of binding agent.
Weight of Resistivity Binding Agent (Qcm) (~) ` 20 280 ' 20 25 ~,.
d. Resistance During Electrolysis Table IV shows -the resistance of the membrane as a function of temperature; this resistance is a measure of the drop in potent-~tial through the membrane.
,~ 30 , ,' `
( ' '`.~
TABLE IV
T ( C~ R (Qcm ) 5.8xlO-83 2.8xlO-105 2.5xlO-l Since the resistance of the membrane remains constant as a function of current density, it is possible, for instance, to allow an electrolytic cell to work at 10 to 15 kAm 2 at tempera-tures higher than 100C with a drop in potential through the membrane that is only 0.15 V to 0.25 V.
e. Stability The membrane maintains its physico-chemical and electrochemical characteristics up to 150C in a highly concentrated alkaline medium, contrary to the organic ion exchange membranes in current use.
f. Gas Separating Character From the volume of the pores and the distribution thereof, as determined by means of the N2-adsorption isotherm (BET method), it was determined that, for the polyantimonic acid powder used in the tests, the grains were free from internal porosity and had a diameter less than 500 Angstr~m. However, these grains form conglomerates which may have diameters of tens of microns. If such macro-grains, the diameter of which ranges from 212 ~m to 38~m, are used as a starting material and they are mixed with polytetrafluoroethene in a ratio of 80/20, 18~ of H2 will be found in the oxygen gas flow during the electrolysis of water at atmospheric pressure. If, however, grains with a dimension smaller than 38 ~m are used as the startins material, 1 to 2% of H2 will be found in -the oxygen gas flow, the working conditions . ~
~13Z097 being the same. For the membrane to act as a gas separator, the size of the macro-grains must not exceed a certain upper limit.
Use Of The Membrane In An Electrolytic Cell The details given below are for the electrolysis of water which is dissociated into hydrogen and oxygen, but the application of the membrane is not limited to this use.
The electrolytic cell shown in Fig. 1 comprises a con-tainer 1 which is divided into chambers 2 and 3 by a unit. This unit comprises an electrode 4 acting as a cathode, the membrane 5, described above, and an electrode 6 acting as an anode. The electrodes 4 and 6 are connected to a potential source 9 by the conductors 7 and 8, respectively, which pass through the wall of the container 1.
The chambers 2 and 3, which are filled with electro-lyte, each form a part of two liquid circuits (no* shown). The products resulting from the electrolysis are recovered in those circuits outside the chambers 2 and 3.
ln chamber 2 the liquid flows from the inlet 10 to the outlet 11. Outside the chamber, the outlet 11 is connected to the inlet 10 through a pipe system, a pump and apparatus for re-covering the products developed by the electrolysis; the pipe system, pump and recovery apparatus are not shown.
In chamber 3 the liquid flows from the inlet 12 to the outlet 13. Outside the chamber, the outlet 13 is connected to the inlet 12 through a pipe system, a pump and apparatus for recovering the products developed by the electrolysis; the pipe system, pump and recovery apparatus are not shown.
If -the liquid is alkaline, the electrochemical re-actions are as follows, according to -the generally accepted g '~
1~3Z097 theory:
at the cathode : 4 H2O + 4 e ~ 4 OH + 2 H2 at the anode 2 2 thus, the resultant reaction is ; 2 H2O ~ 2 H2 + 2 The electrons (e ) are transported through the potent-ial source 9 from the anode 6 towards the cathode 4. The elec-tric circuit is closed by ionic conduction through the membrane 5.
Thus, the mernbrane 5 ensures ionic conduction from one electrode to the other; furthermore, the membrane also separates the gases resulting from the electrolysis.
The ionic conduction takes place by cations and/or anions, depending on the capacity of the membrane for exchanging either anions or cations. The selectivity of the membrane for ions determines whether the majority of the current is transport-ed in the membrane by the cations or anions. Thus, with poly-antimonic acid in a KOH medium, it is mainly the K ions that will migrate from the anode 6 towards the cathode 4, whilst in a NaOH medium it is mainly the Na ions which migrate.
In order to ensure the separation of gases, the mem-brane has a finite thic~ness depending on its composition and on the type and amount of binding agent it contains. The optimum thickness of a membrane comprising 20% by weight of polytetra-; fluoroethene, as a binding agent, is, for instance, 200 microns.
` The electrodes 4 and 6 between which the membrane is - located in close contact therewith to form a unit can be prepared` in a number of different ways.
In the unit shown in Fig. 2, the electrode acting as the cathode is made from a gauze 15 and an electrically conduct-ing coating 14 which acts as a catalyst and covers the gauze 15.
-- ~.`' :~32097 The electrode acting as the anode is made from a gauze 17 and an electrically conducting coating 16 which acts as a catalyst and covers the gauze 17. The gauzes 15 and 17 act as conducting collectors for the input and output of current. The unit was prepared as follows:
A 55 mesh nickel wire gauze with a wire thickness of 3701lmand an area of 100 cm2 was used for the collector 15.
Electrolytic platinum was deposited on this gauze, to form the coating 14, using a solution containing 3% by weight of H2PtC16 ; 10 salt. The electrolytic deposition was carried out at room tempe-rature, the current density being kept at 2 kAm 2 for 30 minutes.
In this way, there was formed on the nickel gauze 15 a porous coating of platinum, active as a catalyst, of about 1.5 mg per cm .
The coating 16 was prepared by mixing nickel nitrate and cobalt nitrate in l-butanol and at a stoichiometric ratio in order to obtain NiCo2O4. The collector 17 was made from the same nickel wire gause as was used for collector 15. This gauze was dipped into the NiCo2O4 solution, after which it was dried for 2 or 3 minutes at 250 C in an oven. This operation was repeated ten times and the electrode was finally heated at 350C
and kept for about 10 hours at that temperature. In this way, a coating of NiCo2O4, active as a catalyst, was deposited on the porous nickel. In the unit, the nickel gauzes 15 and 17 will ` ensure the transport of the electrons.
The preparation of the coating 16 was similar to the preparation of mixed oxides for oxygen-evolution-electrodes des-cribed by G. Sing, M.H. Miles and S. Srinivasan, BNL - 20,984 (1975)-- 30 For preparing the membrane 5, 4 g of polyantimonic acid .
powder with a yrain size less than 30 microns and a specific area (BET) of 25 m /g, available under the trade mark POLYAN from Applied Research, 1,080 Brussels, and 1 g of polytetrafluoro-ethene (Du Pont type 6N) were mixed together. ~The preparatiOn - of polyantimonic acid is known, e.g., from Belgian patent No.
649,746). This mixture was agglomerated by rolling to a thick-ness of 300 llm, by about ten passages through a rolling-mill.
The membrane 5 thus formed was placed on top of the gauze 15, precoated with the active catalyst coating 14. The gauze 17 precoated with the active catalyst coating 16 was then placed on top of the membrane 5; and these three layers were formed into a unit of 800 ~m thickness by rolling.
The unit thus prepared was immersed in 6N KOH. By connecting the gauze 15 and the gauze 17 to an external potential source, the fol]owing results were achieved.
The total potential drop (E) through the unit, expres-sed in volts, was measured for current strengths expressed in kilo-ampere per square meter for temperatures of 22C, 50C and 20I (kA/~I )E 22 C (V) E 50 C (V) E 85 C (V) 2 1.61 1.55 1.47
4 1.73 1.65 1.57 6 1.86 1.75 1.63 8 2.00 1.84 1.70 2.14 1.94 1.77 The gauze of the electrodes may be replaced by any type of current collector, for instance, by a perforated plate.
Though the given example relates to the application of a membrane, as described herein, in a unit for an electrolytic cell intended to electrolyse water, the membrane can also be used .
., ~1320g7 in units for other electrolytic cells, for instance, for produ-: cing chlorine, in fuel cells and for the removal of salt from sea-water.
The membrane does not necessarily have to form a unit with the electrodes, but may also be used in a cell when located between the electrodes without being in close contact with them.
.
,~
''`
. . .
Though the given example relates to the application of a membrane, as described herein, in a unit for an electrolytic cell intended to electrolyse water, the membrane can also be used .
., ~1320g7 in units for other electrolytic cells, for instance, for produ-: cing chlorine, in fuel cells and for the removal of salt from sea-water.
The membrane does not necessarily have to form a unit with the electrodes, but may also be used in a cell when located between the electrodes without being in close contact with them.
.
,~
''`
. . .
Claims (8)
1. A membrane for an electrochemical cell, inhibiting the diffusion of gases and allowing ionic conduction, comprising from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of poly-antimonic acid powder, the grain size of said polyantimonic acid powder being less than 33 µm; said membrane being selectively permeable to cations in a basic medium and being selectively permeable to anions in an acidic medium.
2. A membrane as defined in claim 1, wherein said organic binding agent constitutes from about 5 to about 20 weight percent of said membrane, and wherein the grain size of said polyantimonic acid is less than 30 µm.
3. A membrane as defined in claim 1 or 2, wherein said organic binding agent is polytetrafluoroethane.
4. A membrane as defined in claim 1 or 2, wherein one main surface thereof is coated with an electrode.
5. A membrane as defined in claim 1 or 2, wherein two main surfaces thereof are coated with electrodes, one of said electrodes acting as an anode and the other acting as a cathode, and both of said electrodes functioning as catalysts.
6. A membrane as defined in claim 1 or 2, wherein two main surfaces thereof are associated with electrodes without said membrane and electrodes forming an integral unit.
7. An electrochemical cell comprising a membrane in a basic medium said membrane comprising from about 2.5 to about 30 weight percent of an organic binding agent and from about 97.5 to about 70 weight percent of polyantimonic acid powder, the grain size of said polyantimonic acid powder being less than 38 µm; said membrane being selectively permeable to cations in said basic medium and inhibiting the diffusion of gases.
8. An electrochemical cell comprising:
an anode and a cathode chamber each containing a basic electrolyte, said anode chamber being included in a first liquid circuit and said cathode chamber being included in a second liquid circuit, each of said first and second liquid circuits circulating said electrolyte through said anode and cathode chambers, respectively, and recovering gaseous electrolysis pro-ducts from said anode and cathode chambers, respectively;
an integral unit between said anode and cathode chambers comprising an anode, a cathode and therebetween a mem-brane; said anode facing said anode chamber, said cathode facing said cathode chamber and said membrane comprising from about 97.5 to about 70 weight percent of polyantimonic acid powder embedded in from about 2.5 to about 30 weight percent of an organic bind-ing agent, the grain size of said polyantimonic acid powder being less than 38 µm, said membrane thus being selectively permeable to cations and inhibiting the diffusion of gases; and an electric potential source connected to said anode and cathode.
an anode and a cathode chamber each containing a basic electrolyte, said anode chamber being included in a first liquid circuit and said cathode chamber being included in a second liquid circuit, each of said first and second liquid circuits circulating said electrolyte through said anode and cathode chambers, respectively, and recovering gaseous electrolysis pro-ducts from said anode and cathode chambers, respectively;
an integral unit between said anode and cathode chambers comprising an anode, a cathode and therebetween a mem-brane; said anode facing said anode chamber, said cathode facing said cathode chamber and said membrane comprising from about 97.5 to about 70 weight percent of polyantimonic acid powder embedded in from about 2.5 to about 30 weight percent of an organic bind-ing agent, the grain size of said polyantimonic acid powder being less than 38 µm, said membrane thus being selectively permeable to cations and inhibiting the diffusion of gases; and an electric potential source connected to said anode and cathode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE2055602A BE850594A (en) | 1977-01-21 | 1977-01-21 | UNIT FOR AN ELECTROCHEMICAL CELL |
| BE2/55602 | 1977-01-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1132097A true CA1132097A (en) | 1982-09-21 |
Family
ID=3865363
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,851A Expired CA1132097A (en) | 1977-01-21 | 1978-01-12 | Electrolyte cell membrane of polyantimonic acid and organic binder |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5942753B2 (en) |
| BE (1) | BE850594A (en) |
| CA (1) | CA1132097A (en) |
| FR (1) | FR2378106A1 (en) |
| GB (1) | GB1545454A (en) |
| NL (1) | NL183731C (en) |
| NO (1) | NO150689C (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE874961A (en) * | 1979-03-20 | 1979-09-20 | Studiecentrum Kernenergi | PROCESS FOR PREPARING A MEMBRANE, THEREFORE PREPARED MEMBRANE, ELECTROCHEMICAL CELL WITH SUCH MEMBRANE AND USING SUCH ELECTROchemical cell |
| US4236978A (en) * | 1980-02-08 | 1980-12-02 | Rsr Corporation | Stable lead dioxide anode and method for production |
| BE904104A (en) * | 1986-01-27 | 1986-05-15 | Studiecentrum Voor Kernernergi | METHOD FOR MANUFACTURING A DIAPHRAGM AND METHOD MANUFACTURED BY THIS METHOD |
| LU86876A1 (en) * | 1987-05-13 | 1988-06-13 | Euratom | SEPARATOR FILM FOR A MODERATELY TRITRIATED ACIDIC WATER ELECTROLYSER AND METHOD FOR THE PRODUCTION THEREOF |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| USB326985I5 (en) * | 1963-11-29 | |||
| US3437580A (en) * | 1963-11-29 | 1969-04-08 | Mc Donnell Douglas Corp | Preparation of hydrous metal oxide membranes and acid salts thereof |
| SE7603539L (en) * | 1975-03-31 | 1976-10-01 | Kureha Chemical Ind Co Ltd | CATHION CHANGE MEMBRANE |
-
1977
- 1977-01-21 BE BE2055602A patent/BE850594A/en not_active IP Right Cessation
-
1978
- 1978-01-10 NO NO780085A patent/NO150689C/en unknown
- 1978-01-12 CA CA294,851A patent/CA1132097A/en not_active Expired
- 1978-01-16 NL NLAANVRAGE7800522,A patent/NL183731C/en not_active IP Right Cessation
- 1978-01-19 JP JP53003774A patent/JPS5942753B2/en not_active Expired
- 1978-01-20 FR FR7801685A patent/FR2378106A1/en active Granted
- 1978-01-20 GB GB2375/78A patent/GB1545454A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL183731B (en) | 1988-08-01 |
| FR2378106B1 (en) | 1982-02-26 |
| NO150689B (en) | 1984-08-20 |
| JPS53114785A (en) | 1978-10-06 |
| NO150689C (en) | 1984-11-28 |
| FR2378106A1 (en) | 1978-08-18 |
| GB1545454A (en) | 1979-05-10 |
| NO780085L (en) | 1978-07-24 |
| NL183731C (en) | 1989-01-02 |
| BE850594A (en) | 1977-05-16 |
| JPS5942753B2 (en) | 1984-10-17 |
| NL7800522A (en) | 1978-07-25 |
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