GB2045279A - Electrolytic Permionic Membrane Having Attached Electrodes - Google Patents

Abstract

An electrolytic cell has a carboxylic acid permionic membrane 33 interposed between the anolyte NaCl and catholyte H2O, the membrane having electrocatalytic anode 35 and an electrocatalytic cathode 41 on opposite faces thereof. The cathode may be a depolarized cathode, e.g., a peroxy compound depolarized cathode, a redox couple depolarized cathode, or an oxidant- complex depolarized cathode. The cathode may be a boride, e.g., titanium, diboride, an intercalation compound of carbon and fluorine, or a transition metal, e.g., iron, cobalt, or nickel. The electrocatalysts, may be adhered to the permionic membrane by chemdeposition. The anode may be particulate with hydrophobic material. The individual anode particles may be silicon extended. The electrolytic process may be carried out at high pressure whereby to obtain liquid chlorine, which is then separated from the brine. The cell may be horizontal, with internal heat exchange means. In the case of a bipolar cell, the bipolar conductor element may be silicon, or a titanium alloy, and may have heat transfer and reagent feed means incorporated therein. <IMAGE>

Description

SPECIFICATION Solid Polymer Electrolyte Solid polymer electrolyte chlor alkali cells have a cation selective permionic membrane with an anodic electrocatalyst embedded in and on the anodic surface of the membrane, that is in and on the anolyte facing surface of the permionic membrane, and a cathodic hydroxyl evolution catalyst, i.e., a cathodic electrocatalyst, embedded in and on the cathodic surface of the membrane, that is the catholyte facing surface of the permionic membrane. In an alternative exemplification, a cathode depolarizer, also known equivalently as an HO2- disproportionation catalyst, is present on the cathodic surface, that is the catholyte facing surface of the permionic membrane. This HO2- disproportionation catalyst serves to depolarize the cathode and avoid the formation of gaseous hydrogen.

Solid polymer electrolyte chlor alkali bipolar electrolyzers herein contemplated offer the advantages of high production per unit volume of electrolyzer, high current efficiency, high current density, and in an alternative exemplification, the avoidance of gaseous products and the concomittant auxiliaries necessitated by gaseous products.

In the solid polymer electrolytechlor alkali process aqueous alkali metal chloride, e.g. sodium chloride or potassium chloride, contacts the anodic surface of the solid polymer electrolyte. An electrical potential is imposed across the cell with chlorine being evolved at the anodic surface of the solid polymer electrolyte.

Alkali metal ion, e.g. sodium ion or potassium ion, is transported across the solid polymer electrolyte permionic membrane to the cathodic hydroxyl evolution catalyst on the opposite surface of the permionic membrane. The alkali metal ion, e.g. the sodium ion or potassium ion is transported with its water of hydration, but with substantially no transport of bulk electrolyte.

Hydroxyl ion is evolved at the cathodic hydroxyl ion evolution catalyst as is hydrogen. However, in an alternative exemplification, a cathodic depolarization catalyst, i.e., an HO2- disproportionation catalyst, is present in the vicinity of the cathodic surface of the permionic membrane and an oxidant is fed to the catholyte compartment to avoid the generation of gaseous cathodic products.

The accompanying drawings illustrate various aspects of the invention.

Figure 1 is an exploded view of a bipolar, solid polymer electrolyte electrolyzer.

Figure 2 is a perspective view of a solid polymer electrolyte unit of the bipolar electrolyzer shown in Figure 1.

Figure 3 is a cutaway elevation of the solid polymer electrolyte unit shown in Figure 2.

Figure 4 is a cutaway elevation, in greater magnification of the solid polymer electrolyte sheet shown in the unit of Figures 2 and 3.

Figure 5 is a perspective view of the distributor showing one form of electrolyte feed and recovery.

Figure 6 is a cutaway side elevation of the distributor shown in Figure 5.

Figure 7 is a perspective view of one exemplification of the bipolar element shown in Figure 1.

Figure 8 is a cutaway side elevation of the bipolar element shown in Figure 7.

Figure 9 is a perspective view of an alternative exemplification of a bipolar element having heat exchange means passing therethrough.

Figure 10 is a cutaway side elevation of the bipolar element shown in Figure 9.

Figure 11 is a perspective view of an alternative exemplification of a bipolar element having distributor means combined with the bipolar element.

Figure 12 is a cutaway side elevation of the bipolar element shown in Figure 11.

Figure 13 is a schematic cutaway side elevation of the solid polymer electrolyte electrolytic cell.

Figure 14 is a schematic of the solid polymer electrolyte chlor-alkali process.

The chlor alkali cell shown schematically in Figure 14 has a solid polymer electrolyte 31 with a permionic membrane 33 therein. The permionic membrane 33 has an anodic surface 35 with chlorine catalyst 37 thereon and a cathodic surface 41 with cathodic hydroxyl evolution catalyst 43 thereon.

Also shown is an external power supply connected to the anodic catalyst 37 by distributor 57 and connected to the cathodic catalyst 43 by distributor 55.

Brine by which are mean aqueous alkali metal chloride is fed to the anodic side of the solid polymer electrolyte 31 where it contacts the anodic chlorine evolution catalyst 37 on the anodic surface 35 of the permionic membrane 31. The chlorine, present as chloride ion in the solution, forms chlorine according to the reaction: 2Cl~oCI2+2e~ The alkali metal ion, e.g. sodium ion or potassium ion, shown in Figure 14 as sodium ion, and its water of hydration, passes through the permionic membrane 33 to the cathodic side 41 of the permionic membrane 33. Water is fed to the catholyte compartment both externally, and as water of hydration passing through the permionic membrane 31.The stoichiometric reaction at the cathodic hydroxyl evolution catalyst is: H20+e-oOH-+H In an alternative exemplification, a cathode depolarizing catalyst and an oxidant are present whereby to avoid the generation of gaseous hydrogen.

The structure for accomplishing this reaction is shown generally in Figure 13 where electrolytic cell 11 is shown with walls 21 and a permionic membrane 33 therebetween. The permionic membrane 33 has an anodic surface 35 and an anodic electrocatalyst 37 on the anodic surface 35, and a cathodic surface 41 with cathodic electrocatalyst 43 thereon. In an alternative exemplification, a cathode depolarization catalyst, that is an HO2- disproportionation catalyst (not shown) is in the vicinity of the cathodic surface 41 of the membrane 33 whereby to avoid the evolution of hydrogen gas.

Means for conducting electrical current from the walls 21 to the solid polymer electrolyte 31 are as shown as distributor 57 in the anolyte compartment 39 which conducts current from the wall 21 to the anodic chlorine evolution catalyst 37, and distributor 55 in the catholyte compartment 45 which conducts current from the wall 21 to the cathodic hydroxyl evolution catalyst 43.

In a preferred exemplification, the distributors, 55 and 57 also provide turbulence and mixing of the respective electrolytes. This avoids concentration polarization, gas bubble effects, stagnation, and dead space.

In cell operation, brine is fed to the anolyte compartment 39 through brine inlet 81 a and depleted brine is withdrawn from the anolyte compartment 39 through brine outlet 81 b. The anolyte liquor may be removed as a chlorine gas containing froth, or liquid chlorine and liquid brine may be removed together.

Water is fed to the catholyte compartment 45 through water feed means 101 a to maintain the alkali metal hydroxide liquid thereby avoiding deposition of solid alkali metal hydroxide on the membrane 33. Additionally, oxidant may be fed to the catholyte compartment 45, for example when an HO2- disproportionation catalyst is present, whereby to avoid formation of hydrogen gas and to be able to withdraw a totally liquid cathode product.

One particularly desirable cell structure is a bipolar electrolyzer utilizing a solid polymer electrolyte. Figure 1 is an exploded view of a bipolar solid polymer electrolyte electrolyzer. The electrolyzer is shown with two solid polymer electrolytic cells 11 and 1 3. There could however be many more such cells in the electrolyzer 1. The limitation on the number of cells, 11 and 13, in the electrolyzer 1 is imposed by rectifier and transformer capabilities as well as the possibilities of current leakage. However, electrolyzers containing upwards from 1 50 or even 200 or more cells are within the contemplation of the art utilizing presently available rectifier and transformer technologies.

Individual electrolytic cell 11 contains a solid polymer electrolyte unit 31 shown as a part of the electrolyzer in Figure 1, individually in Figure 2, in partial cutaway in Figure 3, and in higher magnification in Figure 4 with the catalyst particles 37 and 43 exaggerated. Solid polymer electrolyte unit 31 is also shown schematically in Figures 13 and 14.

The solid polymer electrolyte unit 31 includes a permionic membrane 33 with anodic chlorine evolution catalyst 37 on the anodic surface 35 of the permionic membrane 33 and cathodic hydroxyl evolution catalyst 43 on the cathodic surface 41 of the permionic membrane 33.

The cell boundaries, may be, in the case of an intermediate cell of the electrolyzer 1, a pair of bipolar units 21 also called bipolar backplates. In the case of the first and last cells of the electrolyzer, such as cells 11 and 13 shown in Figure 1, a bipolar unit 21 is one boundary of the individual electrolytic cell, and end plate 71 is the opposite boundary of the electrolytic cell. The end plate 71 has inlet means for brine feed 81 a, outlet means for brine removal 81 b, inlet means water feed 101 a, and hydroxyl solution removal 101 b. Additionally, when the cathode is depolarized, oxidant feed, not shown would also be utilized. The end plate 71 also includes current connectors 79.

In the case of an monopolar cell, the end units would be a pair of end plates 71 as described above.

The end plate 71 and the bipolar units 21 provide gas tight and electrolyte tight integrity for the individual cells. Additionally, the end plate 71 and the bipolar units 21 provide electrical conductivity, as well as in various embodiments, electrolyte feed and gas recovery.

The bipolar unit 21, shown in Figures 7 and 8 has anolyte resistant surface 23 facing the anodic surface 35 and anodic catalyst 37 of one cell 11. The anolyte resistant surface 35 contacts the anolyte liquor and forms the boundary of the anolyte compartment 39 of the cell. The bipolar unit 21 also has a catholyte resistant surface 25 facing the cathodic surface 41 and cathode catalyst 43 of the solid polymer electrolyte 31 of the next adjacent cell 13 of electrolyzer 1.

The anolyte resistant surface 23 can be fabricated of a valve metal, that is a metal which forms an acid resistant oxide film upon exposure to aqueous acidic solutions. The valve metals include titanium, tantalum, tungsten, columbium, hafnium, and zirconium, as well as alloys of titanium, such as titanium with yttrium, titanium with palladium, titanium with molybdenum, and titanium with nickel.

Alternatively, the anolyte resistant surface may be fabricated of silicon or a silicide.

The bipolar unit 21 may be fabricated of two sheets, plates, or laminates 23, 25. The surface 23 facing the anolyte may be fabricated of a valve metal, as described hereinabove. However, according to one exemplification, the anolyte facing surface 23 of the bipolar unit 21 is fabricated of an alloy of a valve metal characterized by enhanced resistance to hydride formation and crevice corrosion.

One particularly outstanding group of such alloys are alloys of titanium and a rare earth metal or metals. Contemplated rare earth metals include scandium, yttrium, and the lanthanides. The lanthanides are lanthanum, cerium, praesodymium, neodymium, promethium, samerium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Whenever the term "rare earth metals" is used herein, it is intended to encompass scandium, ytterium, and the lanthanides.

The rare earth metal alloying agent may be one or more rare earth metals. For example, it may be scandium or yttrium or cerium, or lanthanum or lanthanum and yttrium or lanthanum and cerium. Most commonly, the rare earth metal alloying addition will be yttrium.

The amount of rare earth metal alloying agent should be at least a threshold amount sufficient to diminish or even dominate the uptake of hydrogen by the titanium. This is generally at least about 0.01 weight percent, although lesser amounts have positive effects. The maximum amount of rare earth metal alloying agents should be low enough to avoid substantial formation of two phase system.

Generally, this is less than about 2 weight percent rare earth metal for the rare earth metals yttrium, lanthium, cerium, gadolinium, and erbium although amounts up to about 4 or even 5 percent by weight thereof can be toleranted without adverse effects, and less than about 7 weight percent rare earth for the rare earth metals scandium and europium, although amounts up to 10 percent by weight may be tolerated without deleterious effects. Generally the amount of rare earth metal is from about 0.01 weight percent to about 1 weight percent, and preferably from about 0.015 weight percent to about 0.05 weight percent.

The titanium alloy may also contain various impurities without deleterious effect. These impurities include iron in amounts normally above about 0.01 percent or even 0.1 percent and frequently as high as 1 percent, vanadium and tantalum in amounts up to about 0.1 percent or even 1 percent oxygen in amounts up to about 0.1 weight percent, and carbon in amounts up to about 0.1 weight percent.

Alternatively, the anolyte facing surface 23 of the bipolar unit may be an isomorphous beta phase alloy of titanium with molybdenum or an isomorphous alloy of titanium with other transition metal, such as palladium, nickel and iron, e.g., where the iron content is less than 0.05 weight percent iron.

Isomorphous alloys of titanium and the above transition metals offer enhanced resistance to crevice corrosion and hydrogen uptake. The amount of the transition metal, i.e., iron, nickel, palladium, or molybdenum, should be high enough to enhance the crevice corrosion resistance and hydrogen uptake resistance but low enough to avoid formation of a second phase.

The catholyte resistance surface 25 may be fabricated of any material resistant to concentrated caustic solutions containing either oxygen or hydrogen or both. Such materials include iron, steel, stainless steel and the like.

The two members 23 and 25 of the bipolar unit 21 may be sheets of titanium and iron, sheets of the other materials specified above, and there may additionally be a hydrogen barrier interposed between the anodic surface 23 and cathodic surface 25, whereby to avoid the transport of hydrogen through the cathodic surface 25 of a bipolar unit to the anodic surface 23 and cathodic surface 25 of the The hydrogen barrier, interposed between the aniocsurface 23 and cathodic surface 25 of the bipolar unit 21, is a material that impedes the flow of hydrogen, e.g., a material with a low hydrogen solubility or permeability. The hydrogen barrier may be a nonconductive material e.g. silicates and glasses, organic resins, and paints. Alternatively, metals having hydrogen barrier properties may be used.Suitable results may be obtained with vanadium, chromium, manganese, cobalt, nickel, copper, zinc, niobium, molybdenum, silver, cadmium, rhodium tantalum, tungsten, iridium, or gold. Best hydrogen barrier results are obtained when the hydrogen barrier coating is molybdenum, rhodium, iridium, silver, gold, manganese, zinc, cadmium, lead, copper or tungsten. Especially preferred is copper.

The hydrogen barrier may be of sheet or plate. Alternatively, it may be a deposited film or coating.

According to a still further exemplification the hydrogen barrier may be detonation clad to one or both members of the bipolar unit 21.

In an alternative exemplification shown in Figures 9 and 10, heat exchanger conduits 121 pass through the bipolar unit 21. These heat exchanger conduits 1 21 carry cool liquid or cool gas to extract heat from the electrolyzer, for example 12R generated heat as well as the heat of reaction. This enables a lower pressure to be used when the electrolyzer is pressurized, as when a liquid chlorine is the desired product or when oxygen is fed under pressure or both.

In a still further exemplification of the bipolar solid polymer electrolyte electrolyzer, shown in Figures 11 and 1 2 the electrolyte feed and distribution function is performed by the bipolar unit 21.

Thus, in addition to or in lieu of distributor 51, line 133 extends from conduit 11 5a to the interior of the bipolar unit 21 then to a porous or open element 1 31 which distrbutes the electrolyte. Analogously for the opposite electrolyte, feed is through pipe 143 to a porous or open surface 141 on the opposite surface of the bipolar unit.

The individual electrolytic cells 11 and 1 3 of bipolar electrolyzer 1 also include distributor means - 51 which may be imposed between the ends of the cell, that is between the bipolar unit 21 or end wall 71 and the solid polymer electrolyte 31. This distributor means is shown in Figure 1 and individualiy in Figures 5 and 6 with the catholyte liquor conduits 1 05a and 1 05b and the catholyte feed 111 a and catholyte recovery 111 b.

The peripheral wall 53 of the distributor 51 is shown as a circular ring. It provides electrolyte tight and gas tight integrity to the electrolyzer 1 as well as to the cells 11 and 13.

The packing, which may be caustic resistant as packing 55, or acidified chlorinated brine and chlorine resistant, as packing 57, is preferably resilient, conductive, and substantially noncatalytic. That is, packing 55 of the catholyte unit, in the catholyte compartment 45 has a higher hydrogen evolution or hydroxy ion evolution over voltage then cathodic catalyst 43 whereby to avoid the electrolytic evolution of cathodic product thereon. Similarly, the packing 57 in the anolyte compartment 39 has a higher chlorine evolution over voltage and higher oxygen evolution over voltage than the anodic catalyst 37 whereby to avoid the evolution of chlorine or oxygen thereon.

The packing 55, and 57 serve to conduct current from the boundary of the cell such as bipolar unit 21 or end plate 71, to the solid polymer electrolyte 31. This necessitates a high electrical conductivity. The conduction is carried out while avoiding product evolution thereon, as described above. Similarly, the material must have a minimum of contact resistance at the solid polymer electrolyte 31 and at the boundaries of the individual cell 11, e.g., end wall 71 or bipolar unit 21.

Furthermore, the distributor packing 55, 57 distributes and difuses the electrolyte in the anolyte compartment 39 or catholyte compartment 45 whereby to avoid concentration polarization, the build up of stagnant gas and liquid pockets, and the build up of solid deposits such as potassium hydroxide or sodium hydroxide deposits.

The packing 55, 57 may be carbon, for example in the form of graphite, carbon felt, carbon fibers, porous graphite, activated carbon or the like. Alternatively, the packing may be metal felt, a metal fiber, a metal sponge, metal screen, graphite screen, metal mesh, graphite mesh, or clips or springs or the like, such clips or springs bearing on the solid polymer electrolyte and on the bipolar unit 21 of the end plate 71.

According to a further exemplification of this invention, the current collector and current distributor means, 51, providing electrical contact between the cell walls, 21,71, and the solid polymer electrolyte 31, may be a sheet of fine gauge screen or mesh, bearing upon the catalyst 37, 43, and electrically and mechanically in series with the end walls 21, 71, of the cell 11. The electrical and mechanical connector may be provided by first and second resilient metal means, the first resilient metal means bearing upon the catalyst 37, 43, and the second resilient metal means bearing upon the end wall 21, 71, of the cell. The two resilient metal means are removably joined. That is they may bear upon each other under compression, or they may be clipped together.Alternatively, the packing 51, 57 may be packing as rings, spheres, cylinders or the like, packed tightly to obtain high conductivity and low electrical contact resistance.

In one exemplification the brine feed 87a and brine withdrawal 87b, as well as the water and oxidant feed 111 a, and catholyte liquor recovery 111 b, may be combined with distributors 51, 51. In such an exemplification the feed 87a and 111 a extend into the packing 55 and 57 and the withdrawal 87b and 111 b extends from the packing 55 and 57.

In an alternative exemplification the reagent feed and product recovery may be to a microporous distributor, for example microporous hydrophilic or microporous hydrophobic films bearing upon the solid polymer electrolyte 31 and under compression by the distributor means 55 and 57. In an exemplification where the feed is to microporous films upon the solid polymer electrolyte 31, the catalyst particles 37 and 43 may be in the microporous film as well as on the surface of the solid polymer electrolyte 35 and 41.

As described above, individual solid polymer electrolyte electrolytic cell 11 and 13 includes a solid polymer electrolyte 31 with a permionic membrane 33 having anodic catalyst 37 on the anodic surface 35 thereof, and cathodic catalyst 43 on the cathodic surface 41 thereof. The boundaries of the cell may be a bipolar unit 21 or an end plate 71, with electrical conduction between the boundaries and the solid polymer electrolyte 31 being by distributor means 51. Reagent feed 87a and 111 a and product recovery 87b and 111 b are also provided. Additionally, there must be provided means for maintaining and providing an electrolyte tight, gas tight seal as gasket 61.While gasket 61 is only shown between walls 71 and bipolar units 21, and the distributors 51, it is to be understood that additionally or alternatively, gasket 61 may be interposed between the distributors 51, and the solid polymer electrolyte 31.

Gaskets in contact with the anolyte compartment 39 should be made of any material that is resistant to acidified, chlorinated brine as well as to chlorine. Such materials include unfilled silicone rubber as well as various resilient fluorocarbon materials.

The gaskets 61 in contact with the catholyte compartment 45 may be fabricated of any material which is resistant to concentrated caustic soda.

One particular satisfactory flow system is shown generally in Figure 1 where the brine is fed to the electrolyzer 1 through brine inlet 81 a in the end unit 71, e.g., with a hydrostatic head. The brine then passes through conduit 83a in the "0" ring or gasket 61 to and through conduit 85a in the distributor 51 on the cathodic side 45 of cell 11, and thence to and through conduit 89a in the solid polymer unit 31 to anodic distributor 51 on the anodic side 35 of the solid polymer 31 of the electrolytic cell 11. At the distributor 51 there is a "T" opening and outlet with conduit 91 a passing through the distributor 51 - and outlet 87a delivering electrolyte to the anolyte chamber.The flow then continues, from conduit 91 a in distributor 51 to conduit 93a in the next "0" ring or gasket through conduit 95a in the bipolar unit 21 and on to the next cell 13 where the fluid flow is substantially as described above. Brine is distributed by the packing 57 in the distributor 51 within the anolyte compartment 39. Distribution of the brine sweeps chlorine from the anodic surface 35 and anodic catalyst 37 to avoid chlorine stagnation.

The depleted brine is drawn through outlet 87b of the distributor 51 to return conduit 91 b e.g. by partial vacuum or reduced pressure. The return is then through return conduit 89b in the solid polymer electrolyte unit 31, the conduit 85b in the cathodic distributor 51, conduit 83b in the "0" ring or gasket 61 to outlet 81 b where the depleted brine is recovered from the electrolyzer 1.

While the brine feed has been shown with one inlet system and one outlet system, i.e. the recovery of depleted brine and chlorine through the same outlets, it is to be understood that depleted brine and chlorine may be separately recovered. It is also to be understood, that depending upon the internal pressure of the anolyte compartment 39 and the temperature of the anolyte liquor within the anolyte compartment, the chlorine may either be a liquid or a gas.

Water and oxidant enter the electrolyzer 1, through inlet 101 a in the end unit 71. The water and oxidant then proceed through conduit 1 03a in the "0" ring or gasket 61 to conduit 1 05a and "T" in cathodic distributor 51 on the cathodic side 45 of cell 11. The "T" outlet includes conduit 1 05a and outlet 11 1 a. Water and oxidant are delivered by outlet 111 a in ring 53 of the distributor 51 to the catholyte resistant packing 55 within the catholyte chamber 45 of cell 11. The cell liquor, that is the aqueous alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, is recovered from the cathodic surface 41 of the solid polymer electrolyte permionic membrane 33 by the water carried into the cell 11. When oxidant is present, liquid is recovered through the outlet 111 b.When there is no oxidant, gas and liquid may both be recovered through 111 b, or, in an alternative exemplification, a separate gas recovery line, not shown, may be utilized.

While, the electrolyzer is shown with common feed for oxidant and water, and with common recovery for gas and liquid, there may be three conduits present, 111 a, 111 b and a third conduit, not shown, for water feed, oxidant feed, and liquid recovery. Alternatively, there may be three conduits 111 a, 111 b and a third conduit, not shown, for water feed, liquid recovery and gas recovery.

Returning to overall flows in the electrolyzer 1, conduit 105a continues to conduit 1 07a of the solid polymer electrolyte unit 31 to conduit 1 09a of the anodic distributor 51 which continues through to conduit 11 3a of the 0 ring or gasket 61 thence to conduit 11 5a of the bipolar unit 21, where the same path through individual cell 13 is followed as in cell 11. Similarly the network may be continued for further cells.

The recovery of product is shown as being from distributor 51 through outlet 111 b to conduit 1 05b thence to conduit 1 03b in the 0 ring or gasket 61 to outlet 101 b in the end wall 71.

While the flow is described as being to and through distributors 51, as described above, the flow could also be through other paths. For example, the inlet or outlet or both could be in the bipolar unit 21 which bipolar unit would carry porous film or outlet pipes from unit 21. Alternatively, the inlet or outlet or both could be part of the solid polymer electrolyte unit 31.

While the flow is described as being in parallel to each individual cell 11 and 13, it could be serial flow. Where serial flow of the brine is utilized, the T, outlet 87-conduit 91 can be an L rather than a T.

In an exemplification where serial flow is utilized, there would be lower brine depletion in each cell, with partially depleted brine from one cell fed to the next cell for further partial depletion. Similarly, where there is serial flow of the catholyte liquor, the T, conduit 105-outlet 111 could be an L.

Where serial flow is utilized the flow could be concurrent with high sodium or high potassium ion concentration gradients across the solid polymer electrolyte 31 or countercurrent with lower sodium or potassium ion concentration gradients across the individual solid polymer electrolyte units 31.

The bipolar electrolyzer may be either horizontally or vertically arrayed, that is the bipolar electrolyzer 1 may have a solid polymer electrolyte units 31 with either a horizontal membrane 33 or a vertical membrane 33. Preferably the membrane 33 is horizontal with the anodic surface 35 on top of the permionic membrane 33 and the cathodic surface 41 on the bottom of the permionic membrane 33. A horizontal design offers various advantages. Under low pressure operation, chlorine bubbles flow up through the anolyte compartment 39. In the catholyte compartment 45, the horizontal configuration prevents the build up of concentrated alkali metal hydroxide on the bottom surface 41 of the permionic membrane 33, while allowing for the bottom surface 41 of the permionic membrane 33 to be wet with alkali metal hydroxide. Additionally, where oxidant is present, especially gaseous oxidant, the horizontal configuration allows the oxidant to be in contact with the cathodic surface 41 of the permionic membrane 33.

The solid polymer electrolyte 31 contains a permionic membrane 33. The permionic membrane 33 should be chemically resistant, cation selective, with anodic chlorine evolution catalyst 37 on the anodic surface 35 and cathodic, hydroxyl evolution catalyst 43 on the cathodic surface 41 thereof.

The permionic membrane 33 used in providing the solid polymer electrolyte 31 may be, for example, a fluorocarbon resin characterized by the presence of cation selective ion exchange groups, the ion exchange capacity of the membrane, the concentration of ion exchange groups in the membrane on the basis of water absorbed in the membrane, and the glass transition temperature of the membrane material.

The fluorocarbon resins herein contemplated have the moieties: -(-CF2-CXX'-)- and

where X is -F, -Cl, -H, or -CF3; X, is -F, -Cl, -H, -CF3 or CF3 (CF2)m-; m is an integer of 1 to 5; and Y is -A, -#-A, -P-A, or --O--(CF2)n(P,Q,R)-A.

In the unit (P, Q, R), P is --CF2)a(CXX')b(CF2)C Q is (-CF2OCXX')d, R is (--CXX'-O-CF2)e, and (P, O, R) contains one or more of P, Q, R.

0 is the phenylene group; n is 0 or 1; an, a, b, c, d and e are integers from 0 to 6.

The typical groups of Y have the structure with the acid group, A, connected to a carbon atom which is connected to a fluorine atom. These include--(--CF2--)x--A, and side chains having ether linkages such as: -O-(-C F2-) xA,

where x, y, and z are respectively 1 to 10; Z and R are respectivelyF or a C~10 perfluoroalkyl group, and A is the acid group as defined below.

In the case of copolymers having the olefinic and olefin-acid moieties above described, it is preferable to have 1 to 40 mole percent, and preferable especially 3 to 20 mole percent of the olefinacid moiety units in order to produce a membrane having an ion-exchange capacity within the desired range.

A is an acid group chosen from the group consisting of --SO3H -COOH -PO3H2, and -P02H2, or a group which may be converted to one of the aforesaid groups by hydrolysis or by neutralization.

In a particularly preferred exemplification of this invention, A may be either-COOH, or a functional group which can be converted to--COOH by hydrolysis or neutralization such as -CN,.

--COF,--COCl,--COOR1,--COOM,--CONR2R3; R, is a C1~1O alkyl group and R2 and R3 are either hydrogen or C, to C10 alkyl groups, including perfluoroalkyl groups, or both. M is hydrogen or an alkali metal; when M is an alkali metal it is most preferably sodium or potassium.

In the exemplification of this invention where A is -CONR2R3,a and where R and R are hydrogen, or a C, to C,0 alkyl group, including a perfluoroalkyl group, the cathodic surface 41 of the permionic membrane 33 may have the ion exchange groups in the carboxylic acid form, while the anodic surface of the permionic membrane has the ion exchange groups in the amide or N-substituted form. The provision of amide groups or N-substituted amide groups on the anodic surface 35 of the permionic membrane 33 serves to render the cathodic surface 35 hydrophobic. This prevents chlorine stagnation on the membrane 33.

The membrane 33 may be converted to an amide or N-substituted amide group during synthesis, or after the catalyst 37 has been deposited thereon or embedded therein, e.g., by reaction with ammonia or an amine.

In an alternative exemplification A may be either -SO3H or a functional group which can be converted to -SO3H by hydrolysis or neutralization, or formed from -SO3H such as -SO3M1, (SO,-- NH)M", --SO,NHH-RR,-NH,, or or-SO2NR4R5NR4R6; M' is an alkali metal; M" is H, NH4, an alkali metal or an alkaline earth metal; R4 is H, Na or K; R5 is a C3 to C6 alkyl group, (R)2NR6, or RrNR6(R2)zNR6; R6 is H, Na, K or --SO,; and R, is a C2-C6 alkyl group.

The membrane material herein contemplated has an ion exchange capacity from about 0.5 to about 2.0 milligram equivalents per gram of dry polymer, and preferably from about 0.9 to about 1.8 milligram equivalents per gram of dry polymer, and in a particularly preferred exemplification, from about 1.1 to about 1.7 milligram equivalents per gram of dry polymer. When the ion exchange capacity is less than about 0.5 milligram equivalents per gram of dry polymer the current efficiency is low at the high concentrations of alkaline metal hydroxide herein contemplated, while when the ion exchange capacity is greater than about 2.0 milligrams equivalents per gram of dry polymer, the current efficiency of the membrane is too low.

The content of ion exchange groups per gram of absorbed water is from about 8 milligram equivalents per gram of absorbed water to about 30 milligram equivalents per gram of absorbed water and preferably from about 10 milligram equivalents per gram of absorbed water to about 28 milligram equivalents per gram of absorbed water, and in a preferred exemplification from about 14 milligram equivalents per gram of absorbed water to about 26 milligram equivalents per gram of absorbed water.

When the content of ion exchange groups per unit weight of absorbed water is less than about 8 milligram equivalents per gram or above about 30 milligram equivalents per gram the current efficiency is too low.

The glass transition temperature is preferably at least about 200C below the temperature of the electrolyte. When the electrolyte temperature is between about 950C and 110 C, the glass transition temperature of the fluorocarbon resin permionic membrane material is below about 900C and in a particularly preferred exemplification below about 700C. However, the glass transition temperature should be above about -80"C in order to provide satisfactory tensile strength of the membrane material. Preferably the glass transition temperature is from about -800C to about 700C and in a particulary preferred exemplification from about minus 800C to about 500C.

When the glass transition temperature of the membrane is within about 200C of the electrolyte or higher than the temperature of the electrolyte the resistance of the membrane increases and the perm selectivity of the membrane decreases. By glass transition temperature is meant the temperature below which the polymer segments are not energetic enough to either move past one another or with respect to one another by segmental Brownian motion. That is, below the glass transition temperature, the only reversible response of the polymer to stresses is strain while above the glass transition temperature the response of the polymer to stress is segmental rearrangement to relieve the externally applied stress.

The fluorocarbon resin permionic membrane materials contemplated herein have a water permeability of less than about 100 milliliters per hour per square meter at 600C in four normal sodium chloride at a pH of 10 and preferably lower than 10 milliliters per hour per square meter at 60 C in four normal sodium chloride of the pH of 10. Water permeabilities higher than about 100 milliliters per hour per square meter, measured as described above, may result in an impure alkali metal hydroxide product.

The electrical resistance of the dry membrane should be from about 0.5 to about 10 ohms per square centimeter and preferably from about 0.5 to about 7 ohms per square centimeter.

Preferably the fluorinated-resin permionic membrane has a molecular weight, i.e., a degree of polymerization, sufficient to give a volumetric flow rate of about 100 cubic millimeters per second at a temperature of from about 150 to about 3000C.

The thickness of the permionic membrane 33 should be such as to provide a member 33 that is strong enough to withstand pressure transients and manufacturing princesses; e.g., the adhesion of the catalyst particles but thin enound to avoid high electrical resistivity. Preferably the membrane is from 10 to 1000 microns thick and in a preferred exemplification from about 50 to about 200 microns thick.

Additionally, internal reinforcement, or increased thickness, or crosslinking may be utilized, or even lamination may be utilized whereby to provide a strong membrane.

In a preferred exemplification, the permionic membrane includes means for carrying anolyte liquor into the interior of the permionic membrane. This prevents crystallization of alkali metal chloride salts within the permionic membrane 33. The means for accomplishing this may include wicking means, for example, extending up to or beyond the anodic catalyst 37. According to a further exemplification, the means for carrying anolyte liquor into the interior of the permionic membrane may include hydrophilic or wettable fibers extending up to or beyond the anode catalyst 37 or even microtubes extending up to or beyond the anode catalyst 37.

As herein contemplated, the means for carrying the anolyte liquor into the interior of the permionic membrane draw water or anolyte liquor into the membrane beyond the water of hydration associated with the electrolytically carried alkali metal ions. This is to prevent the crystallization of alkali metal chloride such as sodium chloride or potassium chloride in the membrane.

In a preferred exemplification the electrocatalysts 37 and 43 and the membrane 33 are one unit.

While this may be provided by having the electrocatalysts 37 and 43 on the distributor packing 55 and 57, with the distributor 55 and 57 maintained in a compressive relationship with the membrane 33, it is preferred to provide a film of the electrocatalyst 37 and 43 on the permionic membrane 33. The film 37, 43 is generally from about 10 microns to about 200 microns thick, preferably from about 25 to about 175 microns thick and ideally from about 50 to about 1 50 microns thick.

The electrocatalyst-permionic membrane unit 31 should have dimension stability, resistance to chemical and thermal degradation, electrocatalytic activity, and preferably the catalyst particles should be finely divided and porous with at least about 10 square meters of surface area per gram of catalyst particle, 43.

Adherence of the catalyst, 37 and 43, to the permionic membrane 33 may be provided by pressing the particles 37, 43 into a molten, semi-molten, fluid, plastic, or thermoplastic permionic membrane 33 at elevated temperatures. That is, the membrane is heated above its glass transition temperature preferably above the temperature at which the membrane 33 may be deformed by pressure alone. According to a still further exemplification, the particles 37 and 43 may be pressed into a partially polymerized permionic membrane 33 or pressed into a partially cross-linked permionic membrane 33 and the polymerization or crosslinking carried forward, for example, by raising or lowering the temperature, adding initiator, adding additional monomer, or the use of ionizing radiation, or the like.

According to a further exemplification of the method of this invention, where further polymerization is carried out, the particles 37, 43 may be embedded in the partially polymerized permionic membrane 33. Thereafter, a monomer of a hydrophobic polymer can be applied to the surface, with, for example, an initiator, and copolymerized, in situ, with the partially polymerized permionic membrane 33, whereby to provide a hydrophobic surface having exposed particles 37, 43.

In this way, the catalyst particles 37, 43 may be present with the hydrophobic surface, e.g., to protect the anodic surface 35 from chlorine, or to protect the cathodic surface 41 from crystallization or solidification of alkali metal hydroxide, or to enhance depolarization as when a cathodic HO2disproportionation catalyst is present on the cathodic surface 41 of the permionic membrane.

According to a further exempiification of this invention, the permionic membrane moieties may be cross linked, e.g., after catalyst particle deposition, to enhance the hydrophobic character of the membrane surface. The cross linking agent which may react during formation or after the anode materials have been deposited on a partially polymerized permionic membrane. Suitable cross linking agents include the divinyl benzenes, e.g., the perfluorinated divinyl benzenes. Other suitable cross linking agents include perfluorinated dienes, as hexafluorobutadiene, octafluoropentadiene including the 1,3, and 1,4 dienes, and decafluorohexadiene, including the 1,3, the 1,4, and the 1,5 dienes. Most commonly the cross linking agent is a divinyl benzene or perfluorinated C4 to C, diene, especially hexafluorobutadiene.

According to an alternative exemplification the anode electrocatalyst 37 may be extended with silicon. That is, where the anode electrocatalyst 37 is a particle, the particles may be coated silicon particles, i.e., silicon particles coated with a suitable chlorine evolution catalyst. Additionally silicon particles, e.g., coated silicon particles, silicide surfaced silicon particles, and silicon particles having a silicon surface, may be on the anodic surface 35 of the permionic membrane 33, both to provide conductivity between anode particles and as an anode catalyst.

According to this exemplification, anode particles are provided having a low overvoltage which comprises an electrolyte resistant electroconductive surface such as metallic platinum or ruthenium oxide on an electroconductive substrate composed partially or completely and preferably predominantly of silicon in the elemental state (as distinguished from silicides which may be regarded as compounds of silicon and another metal). While the silicon is in elemental state it contains impurities, doping agents or additives, e.g., boron phosphorus, etc., or silicides or certain metals dispersed through the silicon which impart conductivity and/or strength to the silicon. The elemental silicon generally is a continuous phase with the other agents dissolved or dispersed therein.

The silicon particles should be electroconductive and should be at least as electroconductive as graphite, e.g., silicon should have a bulk electrical conductivity in excess of 102 (ohm-centimeters)-' and preferably 104 (ohm-centimeters)~1 or higher. Substantially pure silicon, e.g., silicon having a purity in excess of 99.995 atomic percent, is at most a poor conductor, and may even be characterized as a non-conductor having a resistivity of only about 1 ohm-centimeters. It is known that by incorporating small, even trace amounts of boron, phosphorus, or other materials, the resulting silicon composition will be electroconductive.According to this invention it has been found that with proper precaution the silicon substrate can be provided in a form which is inert to anodic attack and such substrates can be effectively used to support the conductive surface.

Elemental silicon containing up to 2 percent or even up to 5 percent boron or up to 2 percent phosphorus and negligible amounts of other impurities have been found to have the desired inertness to anodic attack by aqueous sodium chloride.

The silicon may also contain iron, e.g., up to about 40 weight percent when phosphorus or boron is present, the phosphorus and boron having a corrosion inhibiting effect.

The silicon particles may also contain silicides. Especially preferred are silicides having a catalytic effect or a conductivity enhancing effect, as the silicides of metals of Group IV, V, and VI, e.g., This, SrSia, VSi2, NbSi2,TaSi and WSi2 and the heavy metal silicides, e.g. CrSi, Cr5Si3, CrSi, CrSi2and MoSi2 as well as cobalt silicides CoSi2.

According to a still further exemplification of the method of this invention, the catalysts 37, 43 may be chemically deposited, e.g., by hypophosphite or borohydride reduction, or be electrodeposited on the permionic membrane 33. Additionally, there may be subsequent activation of the catalyst, for example, by codeposition of a leachable material with a less leachable material and subsequent activation by leaching out of the more leachable material.

According to a still further exemplification, a surface of catalyst 37, 43 may be applied to the permionic membrane by electrophoretic deposition, by sputtering, by laser deposition, or by photodeposition.

According to a still further exemplification of the method of this invention, a catalytic coating 37, 43 may be applied to the permionic membrane 33 utilizing a cheiate of a metal which reacts with the acid groups of the permionic membrane 33.

Typically, the catalyst 37,43 on the surface of the permionic membrane 33 is a precious metalcontaining catalyst, such as a platinum group metal or alloy of a platinum group metal or an intermetallic compound of a platinum group metal or oxide, carbide, nitride, boride, silicide, or sulphide of a platinum group metal. Such precious metal-containing catalysts are characterized by a high surface area and the capability of either being bonded to a hydrophobic particle or being embedded in the hydrophobic fiim. Additionally, the precious metal-containing catalyst may be a partially reduced oxide, or a black, such as platinum black or palladium black, or an electrodeposit or chemical deposit.

The catalysts 37, 43 may also be an intermetallic compound of other metals, including precious metals or non-precious metals. Such intermetallic compounds include pyrochlores, delafossites, spinels, perovskites, bronzes, tungsten bronzes, silicides, nitrides, carbides and borides.

Especially desirable cathodic catalysts which may be present on the solid polymer electrolyte permionic membrane 33 include steel, stainless steel, cobalt, nickel, alloys of nickel or iron, compositions of nickel, especially porous nickel with molybdenum, tantalum, tungsten, titanium, columbium or the like, and boride, electrically conductive, electrically active borides, nitrides, silicides and carbides, such as, the platinum-group metal silicides, nitrides, carbides and borides and titanium diboride.

Other cathodic catalysts 43 that may be present on the cathodic surface 41 of the permionic membrane include the platinum group metals, e.g., platinum, palladium, ruthenium, osmium, iridium, and rhodium, both as smooth deposits for as high surface area deposits, e.g., "blacks" having a surface area in excess of 10 square meters per gram.

As herein contemplated, the permionic membrane 33, or one surface thereof, e.g., the anodic surface 35 or cathodic surface 41, is contacted with a reducing agent, a complexing agent, a buffer, and a compound of the metal, or compounds of the metals to be deposited. The reducing agent may be a borohydride reducing agent or a hypophosphite reducing agent. The borohydride solution should contain 1 to 5 grams per liter of borohydride, e.g., sodium or potassium borohydride and preferable 1.5 to 2.5 grams per liter of borohydride.

Where the deposition is on a synthetic permionic membrane, 33, rather than a metal substrate, sequential contact is particularly desirable. In sequential contact the membrane 33, is first contacted with the reducing agent, and thereafter with the compounds of the metals to be deposited.

The method of this invention is advantageous with transition metals, and is particularly advantageous with group VII transition metals. It is especially useful for the codeposition of two Group VIII metals of dissimilar resistance to chemical leachants, and the subsequent leaching of the less resistant metal.

The borohydride is preferably an alkali metal borohydride, as sodium or potassium borohydride.

The transition metal is present in the second solution as a soluble salt, e.g., a citrate, oxalate, glycolate, sulfate, or chloride. The buffer and the complexing agent may be the acid and the alkali metal salt of the same organic union, e.g., sodium citrate and citric acid, sodium oxalate and oxalic acid, and the like.

Alternatively an inorganic acid, e.g., phosphoric acid and sodium phosphite may be used.

The complexing agent and buffer serve to maintain the Group VIII metal ions in solution, e.g., at thepHof6to8.

In a particularly preferred exemplification the cathodic electrocatalyst 43 comprises porous nickel which contains an effective amount, i.e., an overvoltage reducing or overvoltage stabilizing amount of a Group IVB, VB, VIB, or VIIB transition metal. These transition metals include titanium, zirconium, hafnium, vanadium, columbium, tantalum, chromium, molybdenum, tungsten, manganese, technitium, and rhenium. The preferred materials are titanium, zirconium, hafnium, vanadium, columbium, tantalum, molybdenum, and tungsten. Especially preferred are titanium, tantalum, zirconium, and molybdenum.

The nickel is generally above about 50% and less than about 95%, and generally from about 65 to about 90 percent nickel, calculated as nickel metal, basis total weight of the porous active surface.

The second transition metal is present in the porous catalytic surface 43 in a hydrogen overvoltage lowering amount. This is above about 2.5% preferably above about 5%, but below about 50%, and generally from about 10 to about 35 weight percent, calculated as metal, basis total nickel calculated as metal and second transition metal calculated as metal in the surface. Generally, the amount of the second transition metal in the surface is high enough to have a hydrogen overvoltage lowering effect, but low enough to avoid the high overvoltage identified with porous surfaces that are mainly the second transition e.g., titanium, tantalum, zirconium, and molybdenum.

While the mechanism of the hydrogen overvoltage lowering effect of second transition metal is not clearly understood, it is known that porous films of, e.g., molybdenum alone are high in hydrogen overvoltage, but that a low hydrogen overvoltage over extended periods of electrolysis is observed when a second transition metal is hereinabove described, e.g. molybdenum, is used in conjunction with porous nickel. In the case of molybdenum, the molybdenum is believed to depolarize or catalyze one step of the hydrogen evolution process. For this reason, the upper limit of the second transition metal is below the concentration at which the surface has the hydrogen overvoltage properties of the second transition metal, i.e., below about 50 percent and generally below about 35 percent.

The second transition metal itself may be present as the elemental metal that is as elemental molybdenum, titanium, tantalum, zirconium or tungsten having a formal valence of 0, as an alloy with nickel or as an alkali-resistant compound such as a carbide, nitride, boride, sulfide, phosphide, oxide, or other compound that is insoluble in concentrated alkali metal hydroxide. Preferably, the second transition metal is present in the surface 43 with nickel as the elemental metal, an alloy with nickel, or a carbide.

One particularly outstanding cathode 43 of this invention is one having a porous surface 43 of nickel and molybdenum containing about 82 weight percent nickel, and about 1 8 weight percent molybdenum basis total nickel and molybdenum and having a porosity of about .7 and a thickness of about 75 to about 500 micrometers.

According to a further exemplification of the method of this invention, the cathode herein contemplated is prepared by depositing a film of nickel, the second transition metal, and a leachable material on the permionic membrane 33 and thereafter leaching out the leachable material.

The leachable material may be any metal or compound that can be co-deposited with nickel and the second transition metal or with nickel compounds and compounds of the second transition metal and leached out by a strong acid or strong base without leaching outsignificantquantitesofthe nickel or the second transition metal or causing significant deterioration or poisoning of the nickel or the second transition metal.

The film may be deposited on the permionic membrane 33 by electrodeposition of nickel, the second transition metal, and a leachable material, or by codeposition of solid particles, or by chemical deposition for example, by hypophosphite deposition or by borohydride deposition of nickel compounds, compounds of the second transition metal and leachable materials, or even by deposition and thermal decomposition of organic compounds of nickel, the second transition metal, and leachable materials, for example, deposition and thermal decomposition of alcoholates or resinates.

According to one particularly desirable exemplification of the method of preparing the electrode of this invention, fine particles for example, on the order of about 0.5 to 70 micrometers in diameter, of nickel, the second transition metal or a compound thereof, and a leachable material are embedded in a partially polymerized permionic membrane 33 and the polymerization then completed, with leaching of the leachable material either before or after polymerization. Alternatively, the particles may be embedded in a heated thermoplastic permionic membrane 33.

The leachable materials may be present in the particle with the nickel or may be separate particles. Typical leachable compounds include copper, zinc, gallium, aluminum, tin, silicon, or the like.

Especially preferred are nickel particles containing about 3 to about 70 percent nickel, balance aluminum as Raney alloy.

After completion of polymerization of the partially polymerized membrane 33, or cooling of the heated thermoplastic membrane 33, the particles 43 may be leached, e.g., in alkali such as 0.5 normal caustic soda or 1 normal caustic soda, in order to remove the leachable material, e.g., aluminum, and thereafter rinsed with water. It is, of course to be understood that some of the leachable material may remain in the porous electrode surface 43 without deleterious effect. Thus, for example, where Raney nickel-aluminum alloy, and molybdenum are embedded in the membrane 33, the surface may contain nickel, molybdenum, an aluminum, after leaching. The resulting surface, may, for example, contain amorphous nickel, crystalline molybdenum nickel-aluminum alloys and traces of alumina.

According to a still further exemplification of the invention herein contemplated, the surface 43, may contain boron or phosphorus. These materials believed to be deposited during borohydride or hypophosphite deposition, stabilize the voltage characteristics of the cathodic electrocatalyst 43.

The cathodic electrocatalyst, 43, hereinabove described, while useful with perfluorinated ion exchange membranes 33 generally, finds especial utility in ion exchange membranes 33 having carboxylic acid groups as described hereinabove.

The nickel is generally above about 50% and less than about 95% and generally from about 65 to about 90 percent nickel, calculated as nickel metal, basis total weight of the porous active surface.

The second transition metal is present in the porous catalytic surface 43 in a hydrogen overvoltage lowering amount. This is above about 2.5%, preferably above about 5%, but below about 50%, and generally from about 10 to about 35 weight percent, calculated as metal, basis total nickel calculated as metal and second transition metal calculated as metal in the surface. Generally, the amount of the second transition metal in the surface is high enough to have a hydrogen overvoltage lowering effect, but low enough to avoid the high overvoltage identified with porous surfaces that are mainly the second transition, e.g., titanium, tantalum, zirconium, or molybdenum.

While the mechanism of the hydrogen overvoltage lowering effect of the second transition metal is not clearly understood, it is known that porous films of, e.g., molybdenum, alone, are high in hydrogen overvoltage but that a low hydrogen overvoltage over extended periods of electrolysis is observed when a second transition metal as hereinabove described, e.g., molybdenum, is used in conjunction with porous nickel. In the case of molybdenum, the molybdenum is believed to depolarize or catalyze one step of the hydrogen evolution process. For this reason, the upper limit of the second transition metal is below the concentration at which surface has the hydrogen overvoltage properties of the second transition metal, i.e., below about 50 percent and generally below about 35 percent.

The second transition metal itself may be present as the elemental metal that is as elemental molybdenum, titanium, tantalum, zirconium, or tungsten having a formal valence of 0, as an alloy with nickel or as an alkali-resistant compound such as a carbide, nitride, boride, sulfide, phosphide, oxide, or other compound that is insoluble in concentrated alkali metal hydroxide. Preferably, the second transition metal is present in the surface 43 with nickel as the elemental metal, an alloy with nickel, or a carbide.

One particularly outstanding cathode 43 of this invention is one having a porous surface 43 of nickel and molybdenum, containing about 82 weight percent nickel, and about 1 8 weight percent molybdenum basis total nickel and molybdenum and having a porosity of about .7 and a thickness of about 75 to about 500 micrometers.

According to a further exemplification of the method of this invention, the cathode herein contemplated is prepared by depositing a film of nickel, the second transition metal, and a leachable material on the permionic membrane 33 and thereafter leaching out the leachable material.

The leachable material may be any metal or compound that can be co-deposited with nickel and the second transition metal or with nickel compounds and compounds of the second transition metal and leached out by a strong acid or strong base without leaching out significant quantities of the nickel or the second transition metal or causing significant deterioration or poisoning of the nickel or the second transition metal.

The film may be deposited on the permionic membrane 33 by electrodeposition of nickel, the second transition metal, and a leachable material or by codeposition of solid particles, or by chemical deposition for example, by hypophosphite deposition or by borohydride deposition of nickel compounds, compounds of the second transition metal and leachable materials, or even by deposition and thermal decomposition of organic compounds of nickel, the second transition metal, and leachable materials, for example, deposition and thermal decomposition of alcoholates or resinates.

According to one particularly desirable exemplification of the method of preparing the electrode of this invention, fine particles for example on the order of about 0.5 to 70 micrometers in diameter, of nickel, the second transition metal or a compound thereof, and a leachable material are embedded in a partially polymerized permionic membrane 33 and the polymerization then completed, with leaching of the leachable material either before or after polymerization. Alternative particles may be embedded in a heater thermoplastic permionic membrane 33.

The leachable materials may be present in the particle with the nickel or may be separate particles. Typical leachable compounds include copper, zinc, gallium, aluminum, tin, silicon or the like.

Especially preferred are nickel particles containing about 30 to about 70 percent nickel, balance aluminium, as Raney alloy.

After completion of polymerization of the partially polymerized membrane 33, or cooling of the heated thermoplastic membrane 33, the particles 43 may be leached, e.g., in alkali such as 0.5 normal caustic soda or 1 normal caustic soda, in order to remove the leachable material, e.g., aluminum, and thereafter rinsed with water. It is, of course, to be understood that some of the leachable material may remain in the porous electrode surface 43 without deleterious effect. Thus, for example, where Raney nickei-aluminum alloy, and molybdenum are embedded in the membrane 33, the surface 43 may contain nickel, molybdenum and aluminum, after leaching. The resulting surface, may for example, contain amorphous nickel, crystalline molybdenum, nickei-aluminum alloys, and traces of alumina.

In the electrolysis of alkali metal chloride brines, such as potassium chloride and sodium chloride brines in solid polymer electrolytic cell, especially one having carboxylic acid-type permionic membrane, 33, purity of the brine is of significant importance. The content of transition metals in the brine should be less than 40 parts per million, and preferably less than 20 parts per million, whereby to avoid fouling the permionic membrane 33. The pH of the brine should be low enough to avoid precipitation of magnesium ions. The calcium content should be less than 50 parts per billion, and preferably less than 20 parts per billion.The brine should be substantially free of organic carbon compounds, especially where the chlorine is to be recovered directly from the cell as a liquid and ulitized in a further process, for example, an organic synthesis process such as a vinyl chloride manufacturing process, without further treatment. The brine treatment may be carried out by various methods in order to attain the degrees of purity called for. For example, phosphate precipitation may be used to remove calcium, for example, as the calcium apatite or as a calcium fluoroapatite. Additionally, an ion exchange resin can be utilized to purify the brine.

Preferably the ion exchange resin is a chelating ion exchange resin. In this way the multifunctionality removes multivalent metal impurities, e.g., alkaline earth metal ions and transition metal ions.

The water fed to the catholyte compartment 45 should be substantially free of carbon dioxide and carbonates whereby to prevent the formation and deposition of carbonate on the permionic membrane 33. Preferably, the feed is deionized water.

The recharging or regeneration of the chelating ion exchange resin is critical. The regeneration by the non-oxidizing acid should remove almost all multi-valent cations. This may be accomplished by, e.g., utilizing 10 to 2 bed volumes of 0.5 to 5 normal hydrochloric acid, and preferably 10 to 20 or more bed volumes of 2 to 3 normal hydrochloric acid as the regenerating fluid.

Dilute mineral acids, e.g., from about 0.1 to 10 normal, and preferably from about 0.5 to 5 normal are utilized as the regenerants. Non-oxidizing acids are preferred to avoid damage to the resin. Suitable acids include the hydrogen halides, especially hydrochloric acid.

The strength of the acid should be high enough to withdraw cations from the resin, i.e., above about 0.1 normal, and preferably above about 0.5 normal, but low enough to avoid dehydrating the membrane, i.e., below about 10 normal. In this way a brine may be obtained that contains less than 20 parts per million transition metals, and less than 20 parts per billion alkaline earth metals.

In the operation of the cell, short residence time in the anolyte compartment 39 for the brine depletion of about 10 to about 1 5 percent allows the utilization of brine as a coolant and avoids concentration polarization. However, higher brine depletions, for example, 30, 40, even 50, 60 or 70 percent, may be utilized.

The temperature of the cell may be above 9 degrees C., especially when the brine is low in pH whereby to reduce chlorine hydrate formation. Alternatively, the temperature of the cell may be maintained below 90C., whereby to enhance chlorine hydrate formation and allow the recovery of a slurry of brine and chlorine hydrate.

The cell temperature should be low enough so that when liquid chlorine is recovered from a pressurized cell the pressure necessary to maintain the chlorine liquid is low enough to still permit conventional construction techniques rather than high pressure techniques to be utilized. The pressuretemperature data of liquid chlorine is reproduced in Table I.

Table I Vapor Pressure of Liquid Chlorine Gage Pressure, Temperature Pounds per OC. F. Square Inch -30 -22 3.1 -25 -13 7.2 -20 -4 13.4 -15 +5 17.2 -10 14 23.5 -5 23 30.6 0 32 38.8 +5 41 47.8 10 50 58.2 15 59 68.9 20 68 81.9 25 77 95.4 30 86 111.7 35 95 129.9 40 104 149.0 45 113 170.8 50 122 193.1 55 131 218.1 Table 1 (could.) 60 140 243.8 65 149 271.0 70 158 302.4 75 167 335.7 80 176 370.9 85 185 409.1 90 194 448.8 95 203 492.2 100 212 536 105 221 586 110 230 638 115 239 694 120 248 756 125 257 822 130 266 888 135 275 960 140 284 1035 When the electrolyzer is operated to recover liquid chlorine, the pressure should be high enough to maintain the chlorine liquid.In this way, liquid chlorine and depleted brine may be recovered together, the liquid chlorine separated from the brine, the brine then cooled to convert any chlorine therein to chlorine hydrate, which is further separated from the brine, and the brine refortified in salt, repurified and returned to the cell while the chlorine hydrate separated therefrom is heated to form chlorine.

The pressure in the electrolyzer should be high enough to allow gaseous nitrogen and oxygen to be vented from the cell and the cell auxiliaries, without evaporating significant amounts of liquid chlorine. When operating to produce liquid chlorine the temperature of the cell should be below about 1000C., whereby to maintain the design pressure on the electrolyzer below about 600 pounds per square inch gauge. Preferably, the temperature of the cell should be below about 500 C. whereby to allow design pressure of the cell to be below about 200 pounds per square inch. However, the desired temperature and pressure of the cell may depend upon the end use of the liquid chlorine and the required vapor pressure and temperature of the liquid chlorine.As a practical matter, the pressure within the cell is dependent more upon the pressure of the auxiliaries and end use of the chlorine rather than the structural components of the cell.

High pressure is particularly advantageous, on the catholyte side 45 of the individual electrolytic cell 11, where the cathodic reaction is depolarized, as the high pressure serves to force the depolarizer into the catalyst 43 and disproportionate the HO2-.

When the electrolyzer 1 is operated at a high enough pressure to form liquid chlorine within the anolyte compartments 37, the chlorine and the depleted brine may be recovered from the electrolyzer's liquids. Liquid chlorine is relatively immiscible with brine at the pressures herein contemplated. For this reason the liquid chlorine may be easily separated from the brine, as by centrifugation, filtration, or other viscosity, surface tension, or density dependent means.

Thereafter the separated liquid chlorine may be stored or utilized as liquid without liquefaction.

However, the liquid chlorine constitutes-only 2 to 5 mole percent of the liquids handled in the anolyte compartment. While most of the chlorine will be recovered and separated as a substantially pure liquid, some will be solubilized in the brine. The chlorine in the brine may be recovered by cooling the brine to 900, e.g., by liquid chlorine evaporation cooling, whereby to convert the soluble chlorine contained in the brine to chlorine hydrate. The chlorine hydrate, a yellow crystalline material, may be separated from the depleted brine, and e.g., heated to form chlorine.

In the operation of the cell, the removal of stagnant chlorine pockets from the anodic surface and the removal of solid, crystallized, or highly concentrated liquid alkali metal hydroxides from the cathodic surface 41 of the permionic membrane 33 may be carried out utilizing ultrasonic vibration of the permionic membrane 33, or by the use of a pulsed current. Where a pulsed current is utilized it may be pulsed direct current, rectified alternating current, or rectified half-wave alternating current.

Particularly preferred is pulsed direct current having a frequency of from about 10 to about 40 cycles per second, and preferably about 20 to about 30 cycles per second.

The catholyte liquor recovered from the cell typically will contain in excess of 20 weight percent alkali metal hydroxide. Where, as in a preferred exemplification, the permionic membrane 33 is a carboxylic acid membrane, as described hereinabove, the catholyte liquor may contain in excess of 30 to 35 percent, for example 40 or even 45 or more weight percent alkali metal hydroxide.

The current density of the solid polymer electrolyte electrolytic cell 11 may be higher than that in a conventional permionic membrane or diaphragm cell, for example, in excess of 200 amperes per square foot, and preferably in excess of 400 amperes per square foot. According to one preferred exemplification of this invention, electrolysis may be carried out at a current density of 800 or even 1,200 amperes per square foot, where the current density is defined as total current passing through the cell divided by the surface area of one side of the permionic membrane 33.

According to a particularly preferred exemplification of the method of this invention, the cathode may be depolarized whereby to eliminate the formation of gaseous cathodic products. In operation with the depolarized cathode, oxidant is fed to the cathodic surface 41 of the solid polymer electrolyte 31 while providing a suitable catalyst 43 in contact with the cathodic surface 41 of the solid polymer electrolyte 31 whereby to avoid evolution of gaseous hydrogen. In this way, when the electrolyzer, 1, and electrolytic cell, 11, is maintained at an elevated pressure, as described hereinabove, the evolution of gaseous products can be largely avoided, as can the problems associated therewith.

In the process of producing alkali metal hydroxide and chlorine by electrolyzing an alkali metal chloride brine, such as an aqueous solution of sodium chloride or potassium chloride, the alkali metal chloride solution is fed into the cell, a voltage is imposed across the cell, chlorine is evolved at the anode, alkali metal hydroxide is produced in the electrolyte in contact with the cathode, and hydrogen may be evolved at the cathode. The overall anode reaction is: 2Cl-Cl2+2e (1) while the overall cathode reaction is: 2H20+2eH2+20H (2) More precisely, the cathode reaction is reported to be: H2o+e-~Hads+oH by which the monatomic hydrogen is adsorbed onto the surface of the cathode.In basic media, the adsorbed hydrogen is reported to be desorbed according to one of two alternative processes: 2HadsH2 (4) or H ads +H 2O+e-H2+0H (5) The hydrogen desorption step, i.e., reaction (4) or reaction (5), is reported to be the hydrogen overvoltage determining step. That is, it is the rate controlling step and its activation energy corresponds to the cathodic hydrogen overvoltage. The cathode voltage for the hydrogen evolution reaction (2) is on the order of about 1.5 to 1.6 volts versus a saturated calomel electrode (SCE) on iron in basic media of which the hydrogen overvoltage component is about 0.4 to 0.5 volt.

One method of reducing the cathode voltage is to provide a substitute reaction for the evolution of gaseous hydrogen, that is, to provide a reaction where a liquid product is formed rather than gaseous hydrogen. Thus, water may be formed where an oxidant is fed to the cathode. The oxidant may be a gaseous oxidant such as oxygen, air, or the like. Alternatively, the oxidant may be a liquid oxidant such as hydrogen peroxide, a hydroperoxide, hydrogen peroxide or a peroxy acid or the like.

When the oxidant is oxygen, e.g., as air or as gaseous oxygen, the following reaction is believed to take place at the cathode: Q+2H2O+4e-4OH- (6) This reaction is postulated to be an electron transfer reaction: O,+H,0+2e-HO,-+OH- (7) followed by a surface reaction: 2HO2-oO2+2OH- (8) It is believed that the predominant reaction on the hydrophobic surface is reaction (7), with reaction (8) occurring on the surfaces of the catalyst particles 43 dispersed in and through the cathode surface 41 of the solid polymer electrolyte 33. Such catalyst particles include particles of electrocataiysts as described hereinbelow. In this way, the high overvoltage hydrogen desorption step is eliminated.

Where the oxidant is a peroxy compound, the following reaction is believed to take place at the cathode: RCOO-+2H,0+2e--tRCOH+30H- (9) This reaction is postulated to be an electron transfer reaction followed by a surface reaction.

Suitable organic oxidants are those organic compounds containing a reducible peroxy bond, C0-0-. Suitable oxidants include organic peroxides, organic hydroperoxides, and organic peracids, also referred to as peroxy acids. One preferred group of organic oxidants are organic hydroperoxides.

Particularly outstanding organic oxidants are organic hydroperoxides yielding alcohols that are soluble in water in all proportions, those hydroperoxides yielding alcohols that are of limited solubility in water, and those hydroperoxides yielding alcohols that are sparingly soluble in water. For example, particularly outstanding hydroperoxides are methyl hydroperoxide yielding methyl alcohol, ethyl hydroperoxide yielding ethyl alcohol, n-propyl hydroperoxide yielding n-propyl alcohol, i-propyl hydroperoxide yielding i-propyl alcohol, and t-butyl hydroperoxide yielding t-butyl alcohol.Also useful in the method of this invention are those hydroperoxides yielding alcohols of limited solubility in water such as n-butyl hydroperoxide yielding n-butyl alcohol, sec-butyl hydroperoxide yielding sec-butyl alcohol, i-butyl hydroperoxide yielding i-butyl alcohol, and t-pentyl hydroperoxide yielding t-pentyl alcohol.

Alternatively, those hydroperoxides may be used which yield as cathodic reduction products sparingly soluble alcohols, such as n-pentyl hydroperoxide yielding n-pentyl alcohol, i-pentyl hydroperoxides yielding i-pentyl alcohols, s-pentyl hydroperoxides yielding s-pentyl alcohols, and neopentyl hydroperoxide yielding neopentyl alcohol as cathodic reduction products. Also useful are cumene hydroperoxide yielding cumyl alcohol and ethylbenzene hydroperoxide yielding methyl phenyl carbinol.

Another group of hydroperoxides useful in carrying out the method of this invention are dihydroperoxides. Dihydroperoxides yield glycols as a reaction product when added to the catholyte chamber of an electrolytic cell as herein contemplated. The preferred dihydroperoxides are those that are completely miscible in water or those that are at least partially soluble in water. The preferred dihydroperoxides are the dihydroperoxides of the C3 to C10 alkyls with the dihydroperoxides of the C6 to C,0 alkyls being especially preferred. Such dihydroperoxides include hexane dihydroperoxide, heptane dihydroperoxide, octane dihydroperoxide, nonane dihydroperoxide, and decane dihydroperoxide.

While alcohols, ketones, aldehydes, and glycols are referred to herein, they may only be formed as intermediates and may be further reacted, as by dehydration to give olefines and ethers, or by reaction with other additives as organic acids to yield esters or to yield alkali metal salts of alcohols.

Where the intermediate product is an alcohol, the alcohol may be further reacted to yield ethers.

The aicohol may be separated from the cell liquor and further reacted in order to form the ether, e.g., by reaction with an alkylating agent, e.g., an alkyl sulfate. Thus, where the organic oxidant is tertiary butyl hydroperoxide, the intermediate recovered from the catholyte compartment is tertiary butyl alcohol.

The tertiary butyl alcohol may be removed from the cell, separated from the cell liquor, e.g., by distillation, and reacted with, e.g., methyl sulfate, to yield methyl tertiary butyl ether. Methyl tertiary butyl ether finds utility as an automotive fuel additive.

Particularly desired hydroperoxides are those yielding alcohols that are soluble in water in all proportions and are useful in various industrial processes or example, t-butyl hydroperoxide yielding tbutyl alcohol as a cathodic reaction product, t-butyl alcohol being useful as an automotive anti-knock compound.

Dialkyl peroxides, having the formula R,OOR2 where R and R2 may be -CH3, -C2H5, -C3H7, --C4H9, --CH2CH=CH2, or any other dialkyl peroxide soluble in water or soluble in organic solvents may be used in the method of this invention. In additon to the dialkyl peroxides, the polyoxides having the formula R,OnR2, where n is 3 or 4 may be used in the method of this invention as may the cycloperoxides having the formula R1-O-O-R2.

Peroxy acids, also known as peracids, having the formula R(CO3H) where R may be -H, -CH3, -CH2Cl, -C2H, -(n-C3H7), -(i-C4H9), -(n-C5H11), and any other peracid soluble in water or soluble in organic solvents may be used in this invention. Also, acryl peroxide or other peroxy acid precursors may be utilized in the method of this invention. Additionally, aryl diperoxy acids may be used in the method of this invention.

While the method of this invention is described with respect to organic oxidizers such as organic peroxides, organic hydroperoxides (having the general formula R--OO--O-H) and organic peroxy acids (having the general formula RCO3H), it is to be understood that various derivatives of the organic oxidizers may also be used. For example, the method of this invention may be practised with salts of the organic oxidizers, e.g., salts of organic hydroperoxides (having the formula R-O-O-M) and salts of organic peroxy acids (having the formula RCO3M), where M is a cationic species chosen from the group consisting of alkali metals, alkaline earth metals, and the ammonium radical. Of the alkali metals lithium, sodium, potassium, rubidium, and cesium, most frequently the alkali metal will be sodium or potassium. Of the alkaline earth metals beryllium, magnesium, calcium, strontium, and barium, most frequently the alkaline earth metal will be magnesium or calcium. Generally, when the catholyte liquor is an aqueous alkali metal hydroxide. MOH, the organic oxidizer either is the hydrogen form (e.g., R O-O-H, R--OO--O-R, RCO3H), or the alkali metal salt (e.g., R-O-O-M, RCO3M), where M is the same alkali metal in the hydroxide and the organic oxidizer.

According to the method of this invention utilizing organic peroxy oxidants, the cathode reaction products of the oxidant are recovered from the catholyte chamber 45 along with the cell liquor. The cathodic reduction products of the oxidant may be partially or totally gases or vapors such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, or t-butyl alcohol.Alternatively, the products may be liquids recovered with the cell liquor such as methyl alcohol, ethyl alcohol, n-propyl alcohol, propyl alcohol, t-butyl alcohol, sec-butyl alcohol, i-butyl alcohol, n-butyl alcohol, or t-pentyl alcohol, npentyl alcohol, i-pentyl alcohol, or amyl alcohol or the cathodic product may be emulsions or suspensions or excess amount of sparingly soluble alcohols, such as sec-butyl alcohol, i-butyl alcohol, n-butyl alcohol, t-pentyl alcohol, n-pentyl alcohol, i-pentyl alcohol, or amyl alcohol. Where the cathodic reduction product of the oxidant is recovered either as a gas or as both a gas and a liquid such as method alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, or t-butyl alcohol, the cathodic reduction product is separated from both the water vapor and gas phase and recovered.Alternatively, where the cathodic reduction product of the oxidant is recovered as a liquid, either in solution with water or as suspenion or emulsion in water, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, propyl alcohol, n-butyl alcohol, i-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, t-pentyl alcohol, npentyl alcohol, i-pentyl alcohol, neopentyl alcohol, or s-pentyl alcohol, the cathodic reduction product may be separated from the cell liquor by methods well known in the art such as fractional distillation, extraction, adsorption, stripping, other phase separation techniques, or the like and recovered.

According to one exemplification of this invention, tertiary butyl alcohol is produced during the electrolysis of sodium chloride brine. In this exemplification of the invention, sodium chloride brine is fed to an anolyte chamber 39 of an electrolytic cell 11, tertiary butyl hydroperoxide is fed to a catholyte chamber 45 of the cell and an electrical current is passed from an anode 37 of the cell 11 to a cathode 43 of the cell 11 whereby chlorine is evolved at the anode and tertiary butyl alcohol and acetone are formed in the catholyte chamber. An aqueous catholyte liquor containing sodium hydroxide, tertiary butyl alcohol, acetone, and excess tertiary butyl hydroperoxide is recovered from the catholyte chamber 45 of the cell 11.

Thereafter, an aqueous catholyte cell liquor containing sodium hydroxide, tertiary butyl alcohol, a carbonyl, e.g., acetone, and excess tertiary butyl hydroperoxide, most likely as the sodium salt, is recovered from the cell 11. With a tertiary butyl hydroperoxide feed and a tertiary butyl alcohol product, an azeotrope may be formed upon evaporation and subsequent recovery and distillation of the cell liquor. This azeotrope contains 11.76 percent water and 88.24 percent tertiary butyl alcohol.

In the embodiment of this invention where an excess of tertiary butyl hydroperoxide is fed to the cell, the tertiary butyl alcohol recovered as an azeotrope, the hydroperoxide salt of sodium, e.g., Na+[(CH3)3COO-], may be crystallized out of concentrated aqueous caustic soda solution, e.g., caustic soda solution containing in excess of 40 weight percent caustic soda. This sodium salt of tertiary butyl hydroperoxide may then be recirculated to the catholyte chamber 45 of a cell 11, 13.

According to a further exemplification of this invention, the cell liquor may be fed to another cell 13, for example, to the catholyte chamber 45 thereof, whereby to provide a catholyte liquor enhanced in alkali metal hydroxide content and diminished in organic oxidant content. The remaining organic oxidant may then be further reduced in the subsequent cell or cells, with the cell liquor, in order to produce more by-product, e.g., more ketone, aldehyde, acid, alcohol, or glycol, and a high strength alkali metal hydroxide solution. In this exemplification serial flow of the cathode liquor, e.g., through a bipolar electrolyzer, 1, may be utilized.

According to a still further exemplification of the method of this invention the oxidant may be a redox couple, i.e., a reduction-oxidation couple, where the oxidant is reduced inside the cell and thereafter oxidized outside the cell, as for return to the cell. One suitable redox couple is a copper compound which can be fed to the cell 11 as a cupric compound, reduced to a cuprous compound at the cathode 43, and recovered from the catholyte compartment 45 as a cuprous compound.

Thereafter, the cuprous compound may be oxidized to a cupric compound outside of the electrolyzer 1, and returned to the electrolyzer. Suitable copper couples include chelated copper couples such as phthalocyanines.

According to a further exemplification of the method of this invention, where a redox couple is utilized, the redox couple may be a quinone-hydroquinone redox couple. In this case the quinone is electrolytically reduced to hydroquinone at the cathode 43, hydroquinone is recovered from the catholyte liquor 45, and oxidized to quinone externally of the cell.

According to a further exemplification of the method of this invention, solid oxygen carriers may be fed to the catholyte compartment 45, and recovered partially freed of oxygen. These include manganese (II) complexes, transition metal phthalocyanine tetrasulfonate complexes, and binuclear copper (II) complexes of 1 -phenyl-1 ,3,5-hexane triomate.

The cathode catalysts useful in carrying out the method of this invention are those having properties as HO2- disproportionation catalysts, i.e., catalysts that are capable of catalyzing the surface reaction 2HO2-oO2+2OH- (10) Additionally, the catalyst should either be capable of catalyzing the electron transfer reaction O2+H2O+2e~~HO2-+OH~ (11) or of being used in conjunction with such a catalyst. The catalysts herein contemplated should also be chemically resistant to the catholyte liquor.

Satisfactory HO2- disproportionation catalysts include carbon, the transition metals of Group VIII, being iron, cobalt, nickel, palladium, ruthenium, rhodium, platinum, osmium, iridium, and compounds thereof. Additionally, other catalysts such as copper, lead and oxides of lead may be used. The transition metals may be present as the metals, as alloys, and as intermetallic compounds. For example, when nickel is used, it may be admixed with Mo, Ta, or Ti. These admixtures serve to maintain a low cathodic voltage over extended periods of electrolysis.

Any metal of Group Ill B, IV B, V B, VI B, VII B, I B, II B, or Ill A, including alloys and mixtures thereof, which metal or alloy is resistant to the catholyte can be used as the cathode coating 43 or catalyst on the surface of the membrane 33.

Additionally, solid metalloids, such as phthalocyanines of the Group VIII metals, perovskites, tungsten bronzes, spinels, delafossites, and pyrochlores, among others, may be used as a catalytic surface 43 of the membrane 33.

Particularly preferred catalysts are the platinum group metals, compounds of platinum group metals, e.g., oxides, carbides, silicides, phosphides, and nitrides thereof, and intermetallic compounds and oxides thereof, such as rutile form RuO2-TiO2 having semi-conducting properties.

According to a further exemplification of this invention, the cathode electrocatalyst, that is, the electron transfer catalyst for the reaction H2O+e~oOH~+ H may be a boride of a transition metal. The transition metals providing borides or requisite chemical resistance to concentrated aqueous alkali metal hydroxides, and having surface catalytic activity for the aforementioned reaction are the transition metals of Groups IVB, VB and VIB of periodic table. These metals are titanium, zirconium, hafnium, vanadium, niobium (columbiurn), tantalum, chromium, molybdenum, and tungsten. Preferred among the transition of groups IVB, VB and VIB are those providing borides of higher chemical resistance, e.g., titanium, vanadium, niobium (columbium), tantalum, chromium, and tungsten. Especially preferred is titanium diboride, TiB2.

According to a preferred exemplification of this invention, an intercalation compound of carbon and fluorine may be used as the cathodic catalyst 43.

By an intercalation compound of carbon and fluorine is meant a carbonaceous material crystallized in a graphic layer lattice with the layer atoms being approximately 1.41 angstroms apart, the layers being a greater distance apart, e.g., at least about 3.35 angstroms, and with fluorine atoms present between the layers. As herein contemplated, the carbon layers within the intercalation compound may be puckered, as postulated for carbon monofluoride having the empirical formula (CFx) where x is between 0.68 and 0.995. Alternatively, the carbon layers within the intercalation compound may be substantially planar, as postulated for tetracarbon monofluoride having the empirical formula (CFx where x is between 0.25 and 0.30. Also contemplated herein are various intermediate an nonstoichiometric compounds.

Intercalation compounds of carbon and fluorine are also referred to as fluorinated graphites and graphite fluorides. They are characterized by an infrared spectrum showing an.absorption band at 1220 centimeters~' The carbon-fluorine intercalation compound catalyst 43 herein contemplated may have incorporated therein an H2-disproportionation catalyst.

Where a gaseous oxidant, as air or oxygen is utilized, the portion of the catalyst intended for electron transfer is hydrophilic while the portion intended for the surface reaction may be hydrophilic or hydrophobic and preferably hydrophobic. The surface reaction catalyst is hydrophobic or is embedded in or carried by a hydrophobic film. The hydrophobic film may be a porous hydrophobic material e.g.

graphite or a film of a fluorocarbon polymer on the catalyst. The surface reaction catalyst, as described above, and the electron transfer catalyst should be in close proximity. They may be admixed, or they may be different surfaces of the same particle. For example, a particularly desirable catalyst may be provided by a microporous film on the permionic membrane surface 41 with catalyst 43 carried by a hydrophobic microporous film.

According to a further exemplification of this invention utilizing a depolarized cathode, the electrodes can be weeping electrodes, i.e., electrodes that weep oxidant. In the utilization of weeping electrodes, the oxidant is distributed through the distributor 51 to the catalytic particles 43 thereby avoiding contact with catholyte liquor in the catholyte compartment 45. Alternatively, the oxidant may be provided by a second distributor means, bearing upon the cathodic surface 41 of the permionic membrane 33 or upon the catalytic particles 43.

The feed of oxidant may be gaseous, including excess air or oxygen. Where excess air or oxygen is utilized, the excess air or oxygen serves as a heat exchange medium to maintain the temperature low enough to keep the liquid chlorine vapor pressure low. Alternatively, the use of multiple oxidants, such as air and oxygen, or air and peroxy compound, or oxygen and a peroxy compound, or air or oxygen and a redox couple, may be utilized. Where air or oxygen is used as the oxidant, it should be substantially free of carbon dioxide whereby to avoid carbonate formation on the cathode.

Utilization of a horizontal cell is particularly advantageous where cathode depolarization is utilized. Especially satisfactory is the arrangement where the anodic surface 35 of the permionic membrane 33 and the anodic catalyst 37 are on top of the permionic membrane 31 and the cathodic surface 41 and cathodic catalyst 43 are on the bottom of the permionic membrane 33. This avoids flooding the oxidation catalyst, that is, the HO2- disproportionation catalyst, with alkali metal hydroxide, while providing a thin film of alkali metal hydroxide at the membrane surface 41 adjacent to the cathode surface and enhances the contact of the catalyst 43 and the oxidant While the method of this invention has been described with reference to specific exemplifications, embodiments, and examples, the scope is not to be limited except as limited by the claims appended hereto.

Claims (105)

Claims

1. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having anodic electrocatalyst on the anodic surface thereof and cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; the solid polymer electrolyte being substantially horizontally disposed with the anodic electrocatalyst on the top surface thereof, and the cathodic electrocatalyst on the bottom surface thereof.

2. A method according to claim 1 wherein the permionic membrane is a fluorinated polymeric carboxylic acid permionic membrane.

3. A method according to claim 1 or 2 wherein the solid polymer electrolyte has anodic electrocatalyst facing the anolyte compartment and cathodic electrocatalyst, and hydrogen oxidation catalyst facing the catholyte compartment; oxidant is fed to the catholyte compartment, a film of aqueous alkali metal hydroxide is maintained on the bottom surface of the solid polymer electrolyte, and oxidant is provided at the solid polymer electrolyte surface.

4. An electrolytic cell having a solid polymer electrolyte with anodic electrocatalyst on an anodic surface thereof and cathodic electrocatalyst, means for feeding oxidant, and a hydrogen oxidation catalyst in contact with a cathodic surface of the solid polymer electrolyte, the solid polymer electrolyte being substantially horizontally disposed, with the anodic catalyst on the top surface of the solid polymer electrolyte and the cathodic catalyst and hydrogen oxidation catalyst on the bottom surface.

5. An electrolytic cell having a solid polymer electrolyte with anodic electrocatalyst on an anodic surface thereof and cathodic electrocatalyst on an opposite, cathodic surface thereof, means for feeding oxidant to the cathodic surface of the solid polymer electrolyte, and an HO2- disproportionation catalyst comprising a porous electroconductive substrate having a porous hydrophobic surface thereon in contact with the cathodic surface of the solid polymer electrolyte.

6. A cell according to claim 5, wherein the HO2- disproportionation catalyst comprises a porous carbon substrate with a porous fluorocarbon surface thereon.

7. A cell according to claim 5 or 6, wherein the HO2- disproportionation catalyst is admixed with the cathodic electrocatalyst.

8. A solid polymer electrolyte electrolytic cell having a permionic membrane with a cathode.

bearing upon the cathodic surface thereof, wherein the cathode comprises a boride of a transition metal.

9. A cell according to claim 8, wherein the boride is a boride of titanium, vanadium, niobium, tantalum, chromium, or tungsten.

10. A cell according to claim 9 wherein the titanium boride is TiB2.

11. A method of electrolyzing aqueous alkali metal chloride in an electrolytic cell which comprises feeding the alkali metal chloride to the cell, and imposing an electrical potential across the cell, the cell being a solid polymer electrolyte electrolytic cell according to any of claims 8 to 1 0.

12. A solid polymer electrolyte electrolytic cell having cell walls, a solid polymer electrolyte with electrocatalyst bearing upon at least one surface thereof, current collector means bearing upon the electrocatalyst and the end wall facing the electrocatalyst, the current collector means comprising first resilient metal means bearing upon the electrocatalyst, and second resilient metal means bearing upon the end wall and wherein the first and second resilient metal means are removably joined.

13. An electrolytic cell having a solid polymer electrolyte comprising a permionic membrane comprising a fluorinated cation exchange membrane having carboxylic acid ion exchange groups, anodic electrocatalyst on an anodic surface of the permionic membrane, and cathodic electrocatalyst on a cathodic surface of the permionic membrane, opposite the first surface thereof, the permionic membrane having an ion exchange capacity of about 0.5 to about 2.0 milliequivalents per gram of dry polymer, and a glass transition temperature above about -800C. and below about 900 C.

14. A bipolar electrolyzer comprising a plurality of solid polymer electrolyte electrolytic cells electrically and mechanically in series, each electrolytic cell being as claimed in claim 13.

1 5. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte, withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment.

16. A method according to claim 1 5 wherein the permionic membrane is a fluorocarbon permionic membrane having carboxylic acid in exchange groups.

1 7. A method according to claim 1 5 or 16 wherein the permionic membrane has an ion exchange capacity of about 0.5 to about 2.0 milliequivalents per gram of dry polymer, and a glass transition temperature above about -800C. and about 200C. below the electrolyte temperature.

1 8. A method according to claim 1 7 wherein the polymer has ether linkages in carboxylic acid bearing side chain.

19. A method according to claim 1 5, 16 1 7 or 18 which comprises recovering an alkali metal hydroxide catholyte liquor containing at least 30 weight percent alkali metal hydroxide.

20. A method according to any of claims 1 5 to 19, which comprises maintaining the hydrostatic pressure within the anolyte compartment above the vapor pressure of the evolved chlorine.

21. A method of operating a solid polymer electrolyte bipolar electrolyzer having bipolar units between individual electrolyte cells comprising feeding aqueous alkali metal chloride to an anolyte compartment of an individual cell, feeding water to a catholyte compartment of the individual cell, and passing an electrical current through said cell, at least one of said feeds being fed through heat exchanger means within a bipolar unit of the bipolar electrolyzer being a pair of individual electrolyte cells to extract heat therefrom.

22. A solid polymer electrolyte bipolar electrolyzer having a plurality of individual solid polymer electrolyte electrolytic cells electrically and mechanically in series, wherein each of the cells comprises an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; and wherein each pair of the cells is separated by a bipolar unit therebetween, the bipolar unit comprising an aqueous acid alkali metal chloride resistant surface, and an aqueous alkali metal hydroxide resistant surface, and having a hydrogen barrier interposed between the alkali metal chloride surface and the alkali metal hydroxide surface.

23. An electrolyzer according to claim 22, wherein the hydrogen barrier is vanadium, chromium, manganese, cobalt, nickel, copper, zinc, columbium, molybdenum, silver, cadmium, rhodium, tantalum, tungsten, iridium, or gold.

24. An electrolyzer according to claim 22, wherein the hydrogen barrier is copper.

25. A solid polymer electrolyte bipolar electrolyzer having a plurality of individual solid polymer electrolyte electrolytic cells electrically and mechanically in series, wherein each of the cells comprises an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having anodic electrocatalyst on the anodic surface thereof, and cathodic electrocatalyst on the cathodic surface thereof; and wherein each pair of the cells is separated by a bipolar unit therebetween, the bipolar unit comprising an external electrolyte conduit, and means for transporting electrolyte form the external electrolyte conduit into and through the bipolar unit to a surface of the bipolar unit parallel to the solid polymer electrolyte, the surface having electrolyte distribution means.

26. An electrolyzer according to claim 25 wherein the bipolar unit comprises product recovery means.

27. A method of operating an electrolyzer according to claim 25 or 26, which comprises feeding brine to the anolyte compartments from an external supply, feeding water to the catholyte compartments from an external supply, imposing an electrical potential across the electrolyzer, recovering an anolyte product from the anolyte compartments, and recovering a catholyte product from the catholyte compartments the brine and the water from external supply means being fed into and through the bipolar unit to a surface of the bipolar unit parallel to the solid polymer electrolyte, and through porous means in the bipolar units to the individual solid polymer electrolyte electrolytic cells.

28. A method according to claim 27, comprising recovering product through the bipolar unit.

29. An electrolytic cell having a solid polymer electrolyte comprising a permionic membrane, an anodic electrocatalyst on an anodic surface of the permionic membrane, and a cathodic electrocatalyst on a cathodic surface of the permionic membrane, opposite the anodic surface thereof, the permionic membrane being a fluorinated cation exchange membrane having carboxylic acid groups as the ion exchange groups, and having an ion exchange capacity of about .5 to about 2.0 milliequivalents per gram of dry polymer, a carboxylic acid group concentration of about 8 to about 30 milliequivalents per gram of absorbed water, and a glass transition temperature above about --800C. and below about 700 C. and the anodic surface of the permionic membrane including a cross-linking moiety.

30. An electrolytic cell having a solid polymer electrolyte comprising perfluorocarbon permionic membrane, an anodic electrocatalyst on an anodic surface of the permionic membrane, and a cathodic electrocatalyst on a cathodic surface of the permionic membrane, the solid polymer electrolyte comprising a cross-linking moiety on the anodic surface thereof.

31. A cell according to claim 29 or 30 wherein the cross-linking moiety is derived from perfluorinated diene or divinyl benzene.

32. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte, and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment, the anodic surface of the permionic membrane comprising a cross-linking moiety.

33. A method according to claim 32, wherein the permionic membrane is a perfluorocarbon carboxylic acid permionic membrane.

34. A method according to claim 32, or 33, wherein the cross-linking moiety is derived from a perfluorinated diene or divinyl benzene.

35. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment, the brine containing less than 20 parts per billion calcium and less than 20 parts per million iron.

36. A method according to claim 35, wherein the brine contains less than 40 parts per billion total alkaline earth metals and less than 40-parts per million total transition metals.

37. A solid polymer electrolyte bipolar electrolyzer having a plurality of individual electrolytic cells electrically and mechanically in series with bipolar units therebetween, wherein the anode facing surface of each bipolar unit is an alloy of titanium and, as an alloying agent, molybdenum, palladium, nickel, iron, scandium, yttrium or a lanthanide, the alloying agent being present at a high enough level to diminish hydrogen uptake by the titanium but at a low enough level at avoid substantial formation of a two-phase system.

38. An electrolyzer according to claim 37, wherein the alloying agent is scandium, yttrium or a lanthanide.

39. An electrolyzer according to claim 38, wherein the rare earth metal is yttrium.

40. An electrolyzer according to claim 37, 38 or 39, wherein the alloy comprises from about 0.01 to about 1.0 weight percent of alloying agent.

41. An electrolytic cell for the electrolyzer of aqueous alkali metal chloride having a solid polymer electrolyte comprising a permionic membrane, an anodic electrocatalyst on an anodic surface of the permionic membrane, and a cathodic electrocatalyst on a cathodic surface of the permionic membrane, opposite the anodic surface thereof, the permionic membrane being a fluorinated cation exchange membrane having carboxylic acid groups as the ion exchange groups and having an ion exchange capacity of about 0.5 to about 2.0 milliequivalents per gram of dry polymer, and a glass transition temperature above about -800C. and below about 7O0C., the cell comprising means for withdrawing liquid chlorine with the depleted aqueous alkali metal chloride.

42. A cell according to claim 41 comprising means for recovering chlorine from the depleted aqueous alkali metal chloride.

43. A cell according to claim 42, wherein the means for recovering chlorine from the depleted aqueous alkali metal chloride comprise means for cooling the depleted aqueous alkali metal chloride whereby to form chlorine hydrate, and means to separate the chlorine hydrate from the depleted aqueous alkali metal chloride.

44. An electrolytic cell having a solid polymer electrolyte comprising a permionic membrane, an anodic electrocatalyston an anodic surface of the permionic membrane, a cathodic electrocatalyst on a cathodic surface of the permionic membrane and means for withdrawing liquid chlorine and depleted aqueous alkali metal chloride from the cell, and means for separating the depleted aqueous alkali metal chloride from the liquid chlorine.

45. A cell according to claim 44, comprising means for recovering chlorine from the depleted aqueous alkali metal chloride.

46. A cell according to claim 45 wherein the means for recovering chlorine from the depleted aqueous alkali metal chloride comprise means for cooling the aqueous alkali metal chloride whereby to form chlorine hydrate, and means to separate the chlorine hydrate from the depleted aqueous alkali metal chloride.

47. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a fluorinated cation exchange membrane having carboxylic acid groups as the ion exchange groups, an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte; withdrawing liquid chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; the liquid chlorine being withdrawn from the cell together with depleted aqueous alkali metal chloride and the liquid chlorine being separated from the depleted aqueous alkali metal chloride.

48. A method according to claim 47 comprising recovering chlorine from the depleted aqueous alkali metal chloride.

49. A method according to claim 48 comprising cooling the depleted aqueous alkali metal chloride whereby to form chlorine hydrate, and separating the chlorine hydrate from the aqueous alkali metal chloride.

50. A method according to claim 49, comprising cooling the depleted aqueous alkali metal chloride to below 9 degree Centigrade.

51. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte, withdrawing liquid chlorine and depleted aqueous alkali metal chloride from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; and separating the liquid chlorine from the depleted brine.

52. A method according to claim 51 comprising recovering chlorine from the depleted aqueous alkali metal chloride.

53. A method according to claim 52, comprising cooling the depleted aqueous alkali metal chloride whereby to form chlorine hydrate, and separating the chlorine hydrate from the depleted aqueous alkali metal chloride.

54. A method according to claim 53 comprising cooling the depleted aqueous alkali metal chloride to below 9 degrees Centigrade.

55. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolyte cell having an anolyte compartment separated from a catholyte compartment; imposing an electrical potential across the cell and withdrawing liquid chlorine and depleted aqueous alkali metal chloride from the anolyte compartment and alkali metal hydroxide from the catholyte compartment and separating the liquid chlorine from the depleted aqueous alkali metal chloride.

56. A method according to claim 55 comprising recovering chlorine from the depleted aqueous alkali metal chloride.

57. A method according to claim 56, comprising cooling the depleted aqueous alkali metal chloride whereby to form chlorine hydrate, and separating the chlorine hydrate from the depleted aqueous alkali metal chloride.

58. A method according to claim 57 comprising cooling the depleted aqueous alkali metal chloride below 9 degrees Centigrade.

59. A method of preparing a solid polymer electrolyte comprising: a) providing particles comprising a transition metal and a leachable metal; b) leaching the leachable metal out of the particle, whereby to form a porous particle; c) depositing the porous particle on a permionic membrane whereby to form a solid polymer electrolyte.

60. A method according to claim 59 wherein the transition metal is iron, cobalt or nickel.

61. A method according to claim 59 or 60, wherein the leachable metal is aluminum.

62. A method according to claim 59, 60 or 61, comprising flame spraying an alloy of the transition metal and the leachable metal onto a heat resistant surface, leaching the sprayed particles, and depositing the sprayed, leached particles on the permionic membrane.

63. A method according to claim 62, wherein the sprayed particles adhere to the heat resistant surface and are removed therefrom for deposition on the permionic membrane.

64. A method according to claim 62, wherein the sprayed particles impinge off of the heat resistant surface.

65. A method of electrolysis comprising feeding an aqueous alkali metal chloride to an electrolytic cell having anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte having an anodic electrocatalyst facing the anolyte compartment and a cathodic electrocatalyst facing the catholyte comparment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; providing a cathode depolarization catalyst comprising an intercalation compound of carbon and fluorine on the cathodic side of the solid polymer electrolyte, and feeding an oxidant to the catholyte compartment.

66. A method according to claim 65, wherein the solid polymer electrolyte comprises a fluorinated cation exchange membrane having carboxylic acid groups as the ion exchange group.

67. A method according to claim 66, where the cation exchange membrane has an ion exchange capacity of about 0.5 to about 2.0 milliequivalents per gram of dry polymer and a glass transition temperature above about minus 800 C. but at least about 200 C. below the electrolyte temperature.

68. A method according to claim 65, 66 or 67, wherein the cathode has a hydrophilic portion and a hydrophobic portion in contact with oxidant and wherein the hydrophilic portion comprises the intercalation compound of carbon and fluorine.

69. A method according to any of claims 65 to 68, wherein the oxidant is oxygen.

70. A method according to any of claims 65 to 69, wherein the intercalation compound of carbon and fluorine has the empirical formula CFx where x is from 0.25 to 1.0.

71. A method according to any of claims 65 to 70 wherein the cathode comprises a HO2disproportionation catalyst.

72. An electrolytic cell having a solid polymer electrolyte with an anodic electrocatalyst on an anodic surface thereof and a cathodic catalyst on an opposite, cathodic surface thereof, the electrolytic cell further including means for feeding oxidant to the cathodic surface of the solid polymer electrolyte, and the cathodic catalyst in contact with the cathodic surface of the solid polymer electrolyte comprising an intercalation compound of carbon and fluorine.

73. A cell according to claim 72, wherein the solid intercalation compound of carbon and fluorine has the empirical formula CFx where x is from 0.25 to 1.0.

74. A cell according to claim 72 or 73 wherein the cathodic catalyst in contact with the cathodic surface of the solid polymer electrolyte comprises an HO2- disproportionation compound.

75. A method of electrolysis in an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the polymer electrolyte having an anodic catalyst facing the anolyte compartment and a cathodic catalyst facing the catholyte compartment, which method comprises feeding aqueous alkali metal chloride to the anolyte compartment; feeding an oxidant to the catholyte compartment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; the oxidant being fed to the catholyte compartment in a complex.

76. A method according to claim 75 wherein the complex is a manganese (II) complex, transition metal phthalocyanine tetrasulfonate complex, phosphinomanganese complex or a binuclear copper (II) complex of 1 -phenyl-1 ,3,5-hexane trionate.

77. An electrolytic cell having a solid polymer electrolyte comprising a permionic membrane, an anodic electrocatalyst facing an anodic first surface of the permionic membrane, and a cathodic electrocatalyst on a cathodic surface of the permionic membrane, the cathodic electrocatalyst comprising a first transition series Group VIII metal.

78. A cell according to claim 77 wherein the cathodic electrocatalyst has a surface area of at least 10 square meters per gram.

79. A cell according to claim 77 or 78 wherein the cathodic electrocatalyst further comprises titanium, zirconium, hafnium, vanadium, columbium, tantalum, or tungsten.

80. A cell according to claim 77 or 78 wherein the cathodic electrocatalyst further comprises molybdenum.

81. A cell according to any of claims 77 to 80 wherein the cathodic electrocatalyst further comprises phosphorus or boron.

82. A cell according to any of claims 77 to 81, wherein the permionic membrane is a fluorinated cation exchange membrane having carboxylic acid groups as the ion exchange groups, and having an ion exchange capacity of about 0.5 to about 2.0 milliequivalents per gram of dry polymer, a carboxylic acid group concentration of about 8 to about 30 milliequivalents per gram of absorbed water, and a glass transition temperature above about -800C. and below about 700 C.

83. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell according to any of claims 77 to 82, the solid polymer electrolyte separating an anolyte compartment from a catholyte compartment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment.

84. A method according to claim 83 wherein the solid polymer electrolyte comprises a fluorinated cation exchange membrane having carboxylic acid groups.

85. A method of preparing a solid polymer electrolyte comprising contacting a permionic membrane with a first solution comprising a hypophosphite or a borohydride reducing agent, and thereafter contacting the permionic membrane with a second solution comprising a salt of a metal to be deposited on the permionic membrane, a complexing agent, and a buffer.

86. A method according to claim 85 wherein the metal to be deposited on the permionic membrane is a transition metal.

87. A method according to claim 86 wherein the transition metal is a Group Vlil transition metal.

88. A method according to claim 87 wherein the transition metal is nickel or a platinum group metal.

89. A method according to claim 86, 87 or 88 comprising codepositing a more leachable and a less leachable transition metal on the permionic membrane, and thereafter leaching out the more leachable transition metal.

90. A method of claim 89 comprising codepositing iron and a second Group VIII transition metal on the permionic membrane and leaching out of the iron.

91. An electrolytic cell having a solid polymer electrolyte comprising a permionic membrane, an anodic electrocatalyst on an anodic surface of the permionic membrane, and a cathodic electrocatalyst on a cathodic surface of the permionic membrane, the anodic electrocatalyst comprising silicon extended active catalyst particles.

92. A cell according to claim 91, wherein the silicon extended catalyst particles comprise a silicon core having a catalytic outer surface.

93. A cell according to claim 91, wherein the electrocatalyst comprises silicon particles.

94. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a pe'rmionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; imposing an electrical potential across the solid polymer electrolyte, and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; the anodic electrocatalyst comprising silicon extended catalyst particles.

95. A method according to claim 94, wherein the silicon extended catalyst particles comprise a silicon core having a catalytic outer surface.

96. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte having an anodic electrocatalyst facing the anolyte compartment and a cathodic electrocatalyst facing the cathoiyte compartment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; a cathode depolarization catalyst being provided on the cathodic side of the solid polymer electrolyte, and a peroxide being fed to the "atholyte compartment.

97. A method according to claim 96 wherein the peroxide is hydrogen peroxide, an organic hydroperoxide, organic peroxide, organic peroxy acid or a derivative thereof.

98. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte having an anodic electrocatalyst facing the anolyte compartment and a cathodic electrocatalyst facing the catholyte compartment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; a cathode depolarization catalyst being provided on the cathodic side of the solid polymer electrolyte, and an oxidant of a redox couple being fed to the catholyte compartment.

99. A method according to claim 98, wherein the oxidant is a cupric compound.

100. A method according to claim 99, comprising feeding the cupric compound to the catholyte compartment, and recovering a catholyte liquor containing cuprous ions.

101. A method according to claim 98, wherein the oxidant is quinone.

102. A method according to claim 101 comprising feeding quinone to the catholyte compartment, and recovering a catholyte liquor containing hydroquinone.

1 03. An electrolytic cell having a solid polymer electrolyte with an anodic electrocatalyst on an anodic surface thereof and a cathodic electrocatalyst on an opposite, cathodic surface thereof, the electrolytic cell further including means for feeding oxidant containing particles to the cathodic surface of the solid polymer electrolyte, and a cathodic depolarization catalyst in contact with the cathodic surface of the solid polymer electrolyte.

104. A cell according to claim 103 wherein the oxidant containing particles contain cathode depolarization catalyst.

105. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte having an anodic electrocatalyst facing the anolyte compartment and a cathodic electrocatalyst facing the catholyte compartment; imposing an electrical potential across the solid polymer electrolyte; and withdrawing chlorine from the anolyte compartment and alkali metal hydroxide from the catholyte compartment; a cathode depolarization catalyst being provided on the cathodic side of the solid polymer electrolyte, and oxidant containing particles being fed to the catholyte compartment.