Electrically conductive fibrous web substrate and cathodic element comprised thereof

Abstract

Bonded, coherent fibrous web substrates well adopted as cathodic elements for electrolytic cells and advantageously incorporating an electrocatalytic agent, include a web matrix which comprises a plurality of fibers, at least a portion of which comprising electrically conductive fibers, e.g., carbon fibers, said plurality of fibers being coherently bonded together with a fluorine-containing polymer, and said web substrate having a resistivity of up to about .[∅4 #1# 4.0 Ω.cm.

Description

This application is a continuation of application Ser. No. 623,409 filed Jun. 22, 1984.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a material which is especially adopted for the production of the cathodic element, or cathode, of an electrolysis cell, and particularly an electrolysis cell for aqueous alkali metal halide solutions. The invention also relates to a cathodic element per se, comprising said material. The invention lastly relates to processes for the production of said materials and of said cathodic elements, or cathodes, therefrom.

SUMMARY OF THE INVENTION

Briefly, the present invention features an improved web substrate material comprising a fibrous matrix and a binder therefor, at least a portion of the fibers comprising electrically conductive fibers, the binder therefor comprising a fluorine-containing polymer, and the resistivity thereof being less than about .[∅4 #x2205;6 0.7 0.9 ______________________________________

EXAMPLES 4 to 9

The suspensions described under section (b) of Examples 1 to 3 were used, but these suspensions were filtered through an elementary cathode consisting of:

(i) a net of woven and rolled iron (wire diameter 2 mm, mesh size 2 mm),

(ii) a plate of perforated iron (thickness 1.5 mm, diameter of holes 3 mm, distance between axes 5 mm, quincunx arrangement), or

(iii) a plate of perforated nickel (thickness 1.5 mm, diameter of holes 3 mm, distance between axes 5 mm, quincunx arrangement).

The composite material resulting from this filtration and from fusing the fluorine-containing polymer (12 hours at 100° followed by 10 minutes at 350°) was used, as obtained, as the cathode in a sodium chloride electrolysis cell (operating under 25 A/dm² at 85°C - sodium hydroxide output 120 to 140 g/l).

To carry out the measurements, the diaphragm was placed at 10 mm from the surface of the composite material and the potential of this composite material (cathodic element) was measured using a Luggin probe applied to its surface (9 measurements distributed over 1/2 dm², with the mean potential calculated). The active surface area of the electrolyzer was 1/2 dm².

In this novel cathode, the extra thickness of the web of fibers bonded by means of this fluorine-containing polymer, present on the surface of the elementary cathode, varied from 0.1 to 1 mm depending upon the amount of suspension filtered.

The operating procedures and the measurements are summarized in the table which follows:

In this table ΔUmv/ECS denotes the potential measured on the surface of the composite material (on the fiber web side) or of the cathodic surface relative to a saturated calomel electrode (the potential being expressed in mV).

__________________________________________________________________________
Carbon fibers/
Extra
Elementary        Asbestos fibers
Type of
thickness
No.
cathode     Suspension
(weight)
asbestos
of web (mm)
Binder
Umv/ECs
__________________________________________________________________________
CONTROLS
1  Woven and rolled iron
Elementary cathode only  -1370
2  Perforated iron                            -1380
3  Perforated nickel                          -1430
EXAMPLES
4  Woven and rolled iron
I     63/37   A    1      PFTE -1430
latex
5  Woven and rolled iron
II    63/37   A    1      PFTE -1470
latex
EXAMPLES
6  Woven and rolled iron
II    50/50   A    1      PCTFE
-1450
7  Woven and rolled iron
I     63/37   B    0.1    PTFE -1370
latex
8  Woven and rolled iron
II    50/50   B    0.1    PTFE -1380
powder
9  Perforated nickel
I     63/37   B    0.1    PTFE -1460
latex
__________________________________________________________________________

It will be seen from this table that the composite materials, consisting solely of fibers and the binder, provide, at a very small thickness, a potential substantially equal to the potential measured on the elementary cathode.

The increase in the thickness of the web of fibers also increases the potential, but this increase remains very acceptable.

EXAMPLES 10 to 28

In this series of experiments, the cathodic elements were activated by an electrochemical coating (Examples 10 and 11), by nickeling of fibers (Examples 12 and 13) and by addition of an electrocatalytic element in the form of a powder (Examples 14 to 28), the general technique of manufacture of the composite (elementary cathode+web of fibers) being that of Examples 4 to 9.

(a) The electrochemical coating was carried out as follows: the cathodic element of Example 4 was used as the cathode of an electrolyzer, the anode of which consisted of nickel. The electrolytic bath contained:

______________________________________
(i)  NiCl2.6H2 O = 1 mole/liter
(ii) NH4 Cl = 1 mole/liter
(iii)
ZnCl2 = 15 g/liter
______________________________________

The electrolysis was carried out in a stirred medium, at 20°C, with a current density of 10 A/dm². The operation lasted 30 minutes. After this operation, during which a nickel-zinc alloy was deposited onto the conductive fibers of the cathodic element, the latter was immersed for 2 hours into the electrolytic sodium hydroxide solution (concentration 15 g/l) at 80°C Upon completion of this operation, the zinc had been removed and the amount of nickel deposited represented about 30% of the weight of the web of fibers.

The results were as follows:

__________________________________________________________________________
Potential of the
Comparison
Ratio of carbon
cathodic element
Elementary
Non-activated
Example
fibers/asbestos fibers
(ΔUmv/ECS)
cathode
cathodic element
__________________________________________________________________________
10   63/37      -1.250   -1.370
-1.430
11   50/50      -1.230   -1.370
--
__________________________________________________________________________

(b) In the second activation technique, Example 4 was repeated using either nickeled carbon fibers (63) and asbestos fibers (37), or exclusively nickeled asbestos fibers.

The following results were observed:

______________________________________
Ratio of carbon
Nickeling
Potential of the
fibers/       of the   cathodic element
Examples
asbestos fibers
fibers   (ΔUmv/ECS)
______________________________________
12     63/37         carbon   -1.325
13      0/100        asbestos -1.340
______________________________________

(c) The third activation technique comprised the addition of the electrocatalytic element in powder form.

The procedure was as follows: 1st method (Examples 14 to 16):

A suspension of type I, containing 60 g of PTFE powder, the ratio of carbon fibers/asbestos fibers being either 63/37 or 100/0, was deposited onto an elementary cathode consisting of perforated soft iron (thickness 1.5 mm, diameter of holes 3 mm; distance between axes 5 mm; quincunx arrangement).

A suspension of platinum or a suspension of palladium was filtered through the cathodic element obtained (following the general technique of Examples 4 to 9), under the following conditions:

Platinum suspension (for 1 liter of suspension):

2.4 g of H₂ PtCl₆ were dissolved in 800 cm³ of water containing 1% of α-[4-(1,1,3,3-tetramethyl-butyl)-phenyl]-ω-hydroxy-poly-(oxyet hanediyl), and 0.9 g of sodium borohydride were dissolved in 200 cm³ of water, and these two solutions were mixed under slow stirring.

Suspension of palladium (for 1 liter of suspension):

5.5 g of PdCl₂ were dissolved in 5 cm³ of 3N HCl and diluted to 800 cm³ with water containing 1% of α-[4-(1,1,3,3-tetramethyl-butyl)-phenyl]-ω-hydroxy-poly(oxyeth anediyl), 0.9 g of sodium borohydride were dissolved in 200 cm³ of water, and these two solutions were mixed, under stirring.

After filtration, the cathodic elements were drained, dried (at 100° for 12 hours) and heated at 350° for 10 minutes.

The following results were found:

______________________________________
Ratio of carbon           Potential of the
Ex-   fibers/     Activation    cathodic element
amples
asbestos fibers
Nature    g/dm2
(ΔUmv/ECS)
______________________________________
14    63/37       Platinum  0.2   -1.250 (-1.380)
15    100/0       Platinum  0.2   -1.280
16    63/37       Palladium 0.2   -1.260
______________________________________

In this table, the amount of activator was expressed as weight of platinum or palladium metal deposited per dm² of surface area of the cathodic element.

The value of the potential shown in parentheses was that of the elementary cathode alone. 2nd method (Examples 17 to 28):

Activators in powder form, of particle size equal to or less than 50 μm, were incorporated directly into the suspension.

In the table which follows, the terms or abbreviations have the following meanings:

Type denotes the type of suspension (aqueous or alkaline, as in Examples 1 to 3).

C/A denotes the weight ratio of carbon fibers/asbestos fibers.

P/C+A denotes the weight ratio of fluorine-containing polymer/carbon fibers+asbestos fibers.

Po/A denotes the weight ratio of pore-forming agent/asbestos fibers.

__________________________________________________________________________
Characteristics of the cathodic element      Potential
Pore-                        (Umv/ECS)
forming             Activator
of the cathodic
Example
Type
Polymer agent
C/A P/A + C
Po/A Nature
g/dm2
element
__________________________________________________________________________
17   1  PTFE latex
--   63/37
12/100
0    Pt   0.2 -1250
18   1  "       --   63/37
12/100
0    Ti--Ni
2   -1380
19   1  "       --   63/37
12/100
0    Ti2 --Ni
2   -1290
20   1  "       --   63/37
12/100
0    LaNi5
2   -1320
21   1  "       --   63/37
12/100
0    Mo--Co3
2   -1260
22   1  "       --   63/37
12/100
0    Ni--Al
2   -1280
23   1  "       --   50/50
15/100
0    Ni--Al
2   -1270
24   1  "       --   50/50
15/100
0    Ni--Al
1   -1290
25   1  "       CaCO3
50/50
20/100
100/50
Pt   0.2 -1260
26   1  "       Al2 O3
50/50
20/100
50/50
Pt   0.2 -1240
27   11 PTFE powder
--   63/37
60/100
0    Ti--Ni
2   -1290
28   11 PTFE powder
--   63/27
30/100
0    Ti--Ni
2   -1280
__________________________________________________________________________

EXAMPLES 29 to 40

In the experiments which follow, the cathodic element had been combined with a diaphragm.

(a) Assembly technique:

The cathodic element used was manufactured from an elementary cathode of woven and rolled iron and a suspension of type I, containing a PTFE latex and asbestos fibers (A) and having a ratio of carbon fibers/asbestos fibers of 63/37. This element was activated if desired.

The diaphragm was deposited onto this element by drawing through it, under a programmed vacuum, a suspension comprising:

______________________________________
(i)       H2 O         3.300 g
(ii)      Na sulfosuccinate 1 g
(iii)     Asbestos fibers A 100 g
______________________________________

into which there had been incorporated, after stirring for half an hour,

______________________________________
(iv)    PTFE latex       133 g (latex solids
content = 60%)
(v)     Pore-forming agent
40 g.
(Al2 O3 containing
25% of Al)
______________________________________

the entire mass then having been stirred for half an hour, left to stand for 24 hours, and dispersed and homogenized again for 15 minutes before use.

The deposition under a programmed vacuum was carried out as follows:

(1) 1 minute of settling out

(2) 1 minute under a reduced pressure of 9×10² Pa

(3) 1 minute under a reduced pressure of 7.5×10² Pa

(4) 1 minute under a reduced pressure of 6×10² Pa

(5) 1 minute under a reduced pressure of 5×10² Pa

After the diaphragm had been deposited, the combination of cathodic element and diaphragm was drained and maintained at 100° for 12 hours and then at 350° for 10 minutes.

The pore-forming agent was removed by alkaline treatment before setting up in the electrolyzer.

(b) Use in electrolysis:

The electrolysis conditions were those indicated in the preceding examples except that the inter-electrode distance was reduced to 6 mm.

The following values were measured:

______________________________________
FY             Faraday yield
ΔU (volts)
voltage at the electrolyzer
terminals
NaOH, g/l      concentration on exiting the
electrolyzer.
______________________________________

In addition, the value of ΔU_I→O was measured by plotting ΔU=f(I) or an intensity/potential curve.

The following results were obtained for a constant anodic chloride concentration of 4.8 mole/liter:

__________________________________________________________________________
Cathodic element        Results
Weight       Diaphragm
ΔUI → O
ΔU
NaOH
FY
Example
(kg/m3)*
Activation
kg/m2
volts volts
g/l %
__________________________________________________________________________
29   0.3    --    1.5   2.34  3.45
180 92
30   "      --    "     2.33  3.53
"   94
31   "      --    "     2.34  3.48
"   93
32   0.3    Nickeled
1.5   2.31  3.44
180 94
33   "      carbon
"     2.30  3.36
"   90
34   "      fibers
"     2.31  3.42
"   92
35   0.3          1.5   2.27  3.36
180 93
36   "      Platinum
"     2.22  3.32
"   95
37   "      0.2 g/cm2
"     2.25  3.32
"   92
38   0.3          1.5   2.30  3.40
180 94
39   "      Ni--Al
"     2.25  3.38
"   93
40   "      2 g/cm2
"     2.26  3.30
"   91
__________________________________________________________________________
*except for the elementary cathode

It will be seen from the above results:

At 180 g/l the Faraday yields are of the same order for all of the experiments, namely, about 93%.

The voltage extrapolated to I_O is lowered by activation by nickeling of the fibers and especially in the presence of a catalyst.

______________________________________
Nickeled
Type of activation
Control  fibers    Platinum
Ni--Al
______________________________________
Mean ΔU1 → O
2.34     2.31      2.25   2.27
______________________________________

The voltage at the terminals evidences the same increased voltage gains.

While the invention has been described in terms of various preferred embodiments, the skilled artisan will appreciate that various modifications, substitutions, omissions, and changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the present invention be limited solely by the scope of the following claims.

Claims

#1# 1. A bonded, coherent fibrous web substrate including a fibrous web matrix which comprises a plurality of fibers, at least a portion of which comprising electrically conductive fibers, and a binder consisting of a fluorine-containing polymer, said plurality of fibers being coherently bonded together with said fluorine-containing polymer, and said web substrate having a resistivity of up to about .[∅4 Ω cm. 4.0 Ω.cm.

#1# 41. A bonded, coherent fibrous web substrate including a fibrous web matrix which comprises a plurality of fibers, at least a portion of which comprise electrically conductive fibers, and a binder consisting of a fluorine-containing polymer, said plurality of fibers being coherently bonded together with said fluorine-containing polymer, and said web substrate having a resistivity of up to about .[∅4 Ω cm 4.0 Ω.cm, wherein said web matrix comprises electrically non-conductive fibers having a resistivity in excess of 0.4 Ω cm, the diameters of which being less than about 1 mm and the lengths of which being in excess of about 0.5 mm and electrically conductive fibers.

#1# 2. The web substrate as defined by claim 1, having a resistivity of up to .[∅1 1.0 Ω.cm.

#1# 3. The web substrate as defined by claim 1, said conductive fibers comprising filamentary elements having diameters of less than about 1 mm and lengths in excess of about 0.5 mm.

#1# 4. The web substrate as defined by claim 3, said conductive fibers comprising filamentary elements having diameters ranging from about 10^{-5 to 0.1 mm and lengths ranging from about 1 to 20 mm.}

#1# 5. The web substrate as defined by claim 1, said web matrix comprising electrically non-conductive fibers having a resistivity in excess of 0.4 ω.cm, the diameters of which being less than about 1 mm and the lengths of which being in excess of about 0.5 mm.

#1# 6. The web substrate as defined by claim 5, said non-conductive fibers having diameters ranging from about 10^{-5 to 0.1 mm and lengths ranging from about 1 to 20 mm.}

#1# 7. The web substrate as defined by claim 5, said conductive fibers comprising carbon fibers.

#1# 8. The web substrate as defined by claim 5, said non-conductive fibers comprising asbestos fibers.

#1# 9. The web substrate as defined by claim 5, the weight of said non-conductive fibers comprising up to 90% by weight of the total weight of said conductive fibers plus said non-conductive fibers.

#1# 10. The web substrate as defined by claim 9, the weight of said non-conductive fibers comprising from 20 to 70% by weight of the total weight of said conductive fibers plus non-conductive fibers.

#1# 11. The web substrate as defined by claim 1, said conductive fibers comprising carbon fibers.

#1# 12. The web substrate as defined by claim 1, said binder comprising a fluorinated homo- or copolyolefin.

#1# 13. The web substrate as defined by claim 12, at least some of the fluorinated monomer units comprising said polyolefin being completely fluorosubstituted.

#1# 14. The web substrate as defined by claim 12, at least some of the fluorinated monomer units comprising said polyolefin being completely halosubstituted with fluorine atoms and at least one chlorine, bromine or iodine atoms, or combinations thereof.

#1# 15. The web substrate as defined by claim 12, said fluoropolymer comprising tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene or bromotrifluoroethylene monomer units, or combination thereof.

#1# 16. The web substrate as defined by claim 12, said fluoropolymer comprising up to 75% of ethylenically unsaturated monomer units having at least as many fluorine atoms as carbon atoms.

#1# 17. The web substrate as defined by claim 1, said fluorine-containing polymer binder comprising up to 60% by weight of the total weight of said web.

#1# 18. The web substrate as defined by claim 17, said fluorine-containing polymer binder comprising from 5 to 50% by weight of the total weight of said web.

#1# 19. The web substrate as defined by claim 1, comprising at least one electrocatalytic agent.

#1# 20. The web substrate as defined by claim 19, said at least one electrocatalytic agent comprising particulates having particle sizes ranging from 1 to 100 μm.

#1# 21. The web substrate as defined by claim 20, said electrocatalytic particulates comprising a platinum group metal, or a nickel-zinc, nickel-aluminum, titanium-nickel, molybdenum-nickel, sulfur-nickel, nickel-phosphorus, cobalt-molybdenum, or lanthanum-nickel alloy, or pair thereof.

#1# 22. The web substrate as defined by claim 19, said at least one electrocatalytic agent comprising up to 50% by weight of the total weight of the bonded web.

#1# 23. The web substrate as defined by claim 22, said at least one electrocatalytic agent comprising from 1 to 30% by weight of the total weight of the bonded web.

#1# 24. The web substrate as defined by claim 19, further comprising hydrophilic agents, conductive powders or nonconductive powders.

#1# 25. A web substrate as defined by claim 1 produced by a process comprising formulating a liquid suspension which comprises said fibers and said fluorine-containing polymer binder, forming a fibrous web by elimination of the liquid medium therefrom, and drying the fibrous web thus formed.

#1# 26. The web substrate defined by claim 25, said liquid suspension comprising at least one additive selected from among non-conductive fibers, conductive powder, non-conductive powder, hydrophilic agent, pore-forming agent, and catalytic agent.

#1# 27. The web substrate defined by claim 25, said liquid suspension being formulated by incorporating a dispersion of the fluorine-containing polymer binder into a dispersion of said fibers, the fibers being dispersed in from 1/5 to 1/2 of the final amount of the liquid dispersion medium.

#1# 28. The web substrate defined by claim 25, said fibrous web being formed by filtering said suspension through a highly porous material under programmed vacuum.

#1# 29. The web substrate of claim 28, wherein additives such as conductive powders, nonconductive powders, nonconductive fibers, hydrophilic agents, pore-forming agents and catalytic agents are in suspension and are introduced into said formed web by filtering the suspension through the web.

#1# 30. The web substrate defined by claim 25, comprising drying said fibrous web for from 1 to 24 hours at a temperature of from 70° to 120°C and thence coherently bonding same by heating said dried web at a temperature from 5° to 50°C higher than the melting or softening point of said fluorine-containing polymer for from 2 to 60 minutes.

#1# 31. A cathodic element comprising the web substrate as defined by claim 1.

#1# 32. The cathodic element at defined by claim 31, comprising an electrocatalytic agent.

#1# 33. The cathodic element as defined by claim 31, comprising an electrolysis diaphragm separator.

#1# 34. In an electrolytic cell comprising a cathode and an anode, the improvement which comprises utilizing as the cathode therefor, the cathodic element as defined by claim 31.

#1# 35. A cathodic element comprising a composite of an elementary cathode which includes a metallic surface and the web substrate as defined by claim 1.

#1# 36. The web substrate of claim 1, further comprising a pore forming agent of an alkali metal salt, an alkaline metal salt or amphoteric alumina or silica, which pore forming agents are removable by leaching or chemical or thermal decomposition.

#1# 37. The web substrate of claim 36, wherein the particle size of the pore-forming agent is rom 5-50 μm and used so as to provide a porosity of at least 90% or more.

#1# 38. The web substrate of claim 36, wherein the particle size of the pore-forming agent is from 5-50 μm and used so as to provide a porosity of 90% or less.

#1# 39. The web substrate as defined by claim 1, further comprising hydrophilic agents, conductive powders or nonconductive powders.

#1# 40. The web substrate as defined by claim 39, wherein the hydrophilic agent is sodium dioctylsulfosuccinate.