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3,804,740 N ELECTRO DES HAVING A DELAFOSSTE SURFACE DETAILED DESCRIPTION OF THE INVENTION Cletus N. Welch, Barberton, Ohio, assignor to Nora According to this invention, an electrode is provided International Company, Panama, Panama having a delafossite surface on an electroconductive sub Filed Feb. 1, 1972, Ser. No. 222,501 nt. Cl. B01k3/06; C01b 7/06, 11/26 strate. Delafossites are metal oxycompounds having the U.S. CI. 204-290 R . 3 Claims stoichiometric formula: ABO ABSTRACT OF THE DISCLOSURE where A is platinum, palladium, silver, or copper, and B is chromium, iron, cobalt, rhodium, aluminum, gado Electrodes useful for electrochemical reactions are dis 0 linium, scandium, indium, thallium, lead, ruthenium, and closed. Also disclosed are electrolytic cells utilizing such the lanthanides. B may also be any metal ion having a electrodes and the use of such electrodes in the conduct --3 formal valence state compatible with the delafossite of electrochemical reactions. The electrodes have dela structure. Delafossites also include non-stoichiometric fossite i surfaces on suitable electroconductive bases. compounds having the delafossite-type structure as de Delafossites are electroconductive oxycompounds of 5 fined herein. Delafossites have a unique crystallographic metals and include platinum cobalt delafossite (PtCoO), structure similar to that of the natural mineral delafossite palladium cobalt i delafossite (PdCoO), palladium (CuFeO2) with the slight differences in crystallographic chromium - delafossite (PdCrO2), palladium rhodium structure being due to slightly different ionic radii. delafossite (PdRhO2), palladium ruthenium delafossite Delafossites provide particularly satisfactory electrode (PdRuO2), palladium lead delafossite (PdPbO), the 20 materials because they combine high electrical conductiv palladium lanthanide delafossites, silver cobalt delafossite ity comparable to that of metals, with high resistance (AgCoO2), silver gadolinium delafosssite (AgGaO2), to chemical attack comparable to that of refractory metal silver scandium delafossite (AgScO2), silver indium dela oxides. For example, the bulk electrical conductivity of fossite - (AgInO2), silver thallium delafossite (AgT1O2), compressed powders of the platinum and palladium dela "copper i cobalt delafossite - (CuCoO2) and copper iron 25 fossites is on the order of about 108 to 104 (ohm-centi "delafossite (CuFeO2), includinig the mineral delafossite meters)--1. Such platinum and palladium delafossites are, (CuFeO). . . . . however, resistant to attack by strong acids such as aqua regia at 70° C. and by nascent chlorine. BACKGROUND 30 Delafossites are a family of oxides of two or more Numerous electrochemical reactions, such as the elec metals, the oxide having a rhombohedral structure with trolysis of . brines, hydrochloric acid, and sulfates, elec a hexagonal crystal habit similar to that of the mineral troplating, i electrowinning, electrolytic production of delafossite CuFeO2. Delafossites may further be char metal powders, electrolytic cleaning, electrolytic pickling, acterized in that their crystals have a space group of and the electrochemical generation of electric power, in 35 166, a Shoenflies group of Dadº, a Standard Full Symbol volve the use of non-consumable anodes. Previously, of graphite anodes have been used, especially in such proc esses as , the electrolysis of brines and the electrolysis R (R, bar 3, two over m) of hydrochloric acid. More recently, electrodes have been : developed for such processes utilizing a suitable electro 40 and an International Symbol of conductive base or substrate and an electrocatalytic coat ing thereon. Typically, such electrocatalytic coatings have Ram (R, bar 3, m) been the platinum group metals; e.g., platinum, osmium, iridium, ruthenium, i palladium, and rhodium, and their 45 Such oxides and their crystallography are particularly oxides. * • . " . described in the articles by W. J. Croft et al., Acta SUMMARY OF THE INVENTION Crystallogr., vol. 17, p. 313 (1964); W. Gessner, Z. Anorg. Allg. Chem., vol. 352, p. 145 (1966); H. Hahn It has now been found that a particularly satisfactory et al., Z. Anorg. Allg. Chem., vol. 279, p. 281 (1955); electrode for the conduct of electrochemical reactions W. Dannhauser et al., J. Amer. Chem. Soc., vol. 77, p. may be provided by the use of a delafossite surface on 50 896 (1955); H. Wiedersich et al., Mineral Mag., vol. 36, a suitable electroconductive substrate or base member. p. 643 (1968); A. Krause et al., Z. Anorg. Allg. Chem., Delafossites are oxides of high electrical conductivity vol. 228, p. 352 (1936); A. Pabst, Amer. Mineral, vol. 31, having the stoichiometric formula: p. 539 (1946); and A. H. Muir et al., J. Phys. Chem. Solids, vol. 28, p. 65; R. D. Shannon et al., “Chemistry ABO 55 of Noble Metal Oxides. I. Synthesis and Properties of A is platinum, palladium, silver, or copper. B is typical ABO Delafossite Compounds,” Inorganic Chemistry, vol. ly chromium, iron, cobalt, rhodium, aluminum, gadolini 10, p. 713 (1971); C. I. Prewitt et al., “Chemistry of um, scandium, indium, thallium, lead, ruthenium, and the Noble Metal Oxides. II. Crystal Structures of PtCoO, lanthanides. B may, however, be any metal ion having PdCoO2, CuFeO2, and AgFeO2” Inorganic Chemistry, a stable. --3 formal valence state compatible with the 60 vol. 10, p. 719 (1971); D. B. Rogers et al., “Chemistry delafossite structure. . of Noble Metal Oxides. III. Electrical Transport Prop Delafossites also include i non-stoichiometric com erties and Crystal Chemistry of ABO Compound With pounds isostructural with the stoichiometric delafossites. the Delafossite Structure,” Inorganic Chemistry, vol. 10, A suitable electroconductive substrate is an electrocon p. 723 (1971); U.S. Pat. 3.498,931 to D. B. Rogers et ductive substrate that is substantially not attacked by the 65 al. for “Electrically conductive Oxides Containing Pal electrolyte. ladium and Their Preparation;” U.S. Pat. 3,514,414 to

3,804,740 5 6 These peaks of high intensity are caused by the X-rays For the more compact platinum group metal delafos being “reflected” from parallel planes in the crystal re site i crystals, a peak exists at about 1.76 to 1.81 ang inforcing each other. - The wave length of the X-rays, the stroms. This peak, at about 1.7655 for the platinum co spacing of the planes in the crystal, and the angle, e, are balt delafossite (PtCoO2), has an intensity of about 0.30. related by Bragg’s law. Bragg’s law is: For the palladium cobalt delafossite, the peak appearing at an interplanar distance of about 1.7616 angstroms has 2d sin E9:ssenM an intensity of about 0.30. For the slightly less compact where d is the distance between the planes of the crys palladium chromium delafossite (PdCrO2), the peak ap tal, n is an integer, M is the wave length of the X-rays, pears at about 1.8084 angstroms and has an intensity of and €9 is both the angle of incidence of the X-rays and the less than 0.05. angle of reflection of the X-rays. X-ray diffraction data are obtained from a diffractom TABLE 1 eter that is direct reading in 2e. The quantity (180° X-ray powder diffraction pattern for copper iron minus 269) is the angle between the incident ray and the 5 delafossite (CuFeO) reflected ray. d: - - . . I/IIo Table I shows the X-ray diffraction pattern for the min 286 ------35 eral delafossite (CuFeO). Particularly to be noted is the 2.58 ------18 doublet at 2.58 and 2.508 angstroms and the peaks at 2.508 ------100 2.238 and 1.658 angstroms, respectively. 2.238 ------25 Certain generalities may be noted with respect to the 20 2.083 ------6 powder X-ray diffraction patterns of the platinum group 1902 ------9 metal delafossites. First to be noted is a particularly strong 1-6º8 ------35 peak at a d value from about 5.9072 to 6.0229. Next to i 1.512 ------40 be noted in FIGS. III through V, inclusive, is the existence 1-434 ------20 of a strong doublet where the peaks are separated from 25 1336 ------18 each other by from about 0.06 to about 0.07 angstrom 1295 ------12 with the greater separation of peaks and greater differ 1253 ------10 ences of intensities being for the platinum group metal 1.184 ------6 delafossites having the larger unit crystal and the peaks 1.119 ------10 being closer together and of more. nearly equal intensity 30 1.108 ------6 for the platinum group metal delafossites having the more 1040 ------18 compact unit crystal. For the platinum cobalt delafossite 0.984 ------* 1 6 (PtCoO), the two peaks of the doublet are at 2.4260 and 0.965 ------10 2.3609. angstroms. For the palladium cobalt delafossite (PdCoO), the two peaks of the doublet are at about 35 TABLE 2 2.4272 and 2.3616 angstroms, while for the palladium chromium delafossite the two peaks are at 2.5065 and X-ray powder diffraction pattern for platinum cobalt 2.4375 angstroms, and for the palladium rhodium dela M delafossite (PtCoO) fossite (PdRhO2) the two peaks are at about 2.5884 and d: M I/IIo 2.5141 angstroms. Also to be noted is the increasing dif 40 59450 ------90 ference in intensity, between the two members of the * 2.9728 ------100 doublet proceeding from the more compact to the less 2-4260 ------70 compact unit crystals. The first peak in doublet represents an interplanar space of from about 2.42 angstroms . 45

W (PtCoO) M to about 2.58 angstroms (PdRhO2) while the second peak represents an interplanar space of from about 2.46 ang stroms (PtCoO) to about 2.51 angstroms (PdRhO2). 50 , Further to be noted is a strong peak at from about 2.1460 tó about 2.2644 angstroms. This peak is at about 2.14 angstroms for the more compact unit cell of the platinum cobalt delafossite, at a : spacing of 2.1448 ang stroms for the palladium cobalt delafossite (PdCoO2), at 55 a spacing of 2.2088 for palladium chromium delafossite (PdCrO2), and at 2.26 angstroms for the slightly less TABLE 3. compact unit cell of the platinum rhodium delafossite X-ray powder diffraction pattern for palladium cobalt (PtRhO2). . . . , - : : : : - , delafossite (PdCoO) : Also to be noted is a weak doublet in the range of from 60 2.0185 and 1.9814 angstroms with intensities of 0.30 and d: W * * , , ' , . *: * I/Io 0:40, respectively, for the more compact platinum cobalt 2.9072 ------45 delafossite. As the unit cell increases in size, this particu 2.4272 ------80 har i doublet becomes more spread out and less intense. 2.3616 ------100 For the slightly s less i compact palladium cobalt: dela 65 2, 1448 ------85 fossite, the doublets appear at d spaces of 2.0165 and 2.0165------: * 15 1.9715 angstroms, respectively, and the weaker of the 1.9713 ------50 two has an intensity - of about 0.15. - For the palladium 1.7616 ------30 chromium delafossite (PdCrO2), the weaker of the two 1.6445 ------: -85 members of the doublet has an intensity of about 0.02 70 1.-4788 ------| 35 and the doublets appear at 2.0753 and 2.0089 angstroms, 1.4373 ------70 respectively. For the even less compact palladium ; rho 1.4149 ------65 dium delafossite (PdRhO2), the members of the doublet 1.3762 ------15 appear at 2.1.198 and 2.0088 angstroms, respectively, 1.3474 ------. 15 where they both have intensities of less than, 0.05. . . 75 * 1.2762 ------| 65 3,804,740 7 8 TABLE 4 crystal. The preferred delafossites are those where the monovalent cation has an effective ionic radius of from X-ray powder diffraction pattern for palladium chromium about 5.58 to 0.61 angstrom, such as palladium (-- 1) delafossite (PdCrO2) and platinum (-- 1). d: I/Io 5 The cation represented by B is most commonly chro 6.0229 ------20 mium, iron, cobalt, rhodium, aluminum, gadolinum, scan 3.0137 ------65 dium, indium, thallium, lead, ruthenium, and the lantha 2.5065 ------30 nides (La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, 2.4375 ------100 Yb, and Lu and Y). B is typically a trivalent cation hav 2.2088 ------40 0 ing an effective ionic radius of from about 0.50 angstrom 2.0753 ------2 unit to about 1.05 angstrom units, and most frequently 2.0089 ------10 from about 0.50 angstrom unit to about 0.89 angstrom 1.8084 ------5 unit. The preferred trivalent cations are those having an 1.6864 ------30 effective ionic radius of from about 0.50 to about 0.70 1.5074 ------5 angstrom unit and include cobalt (Co3+), having an ef 1.4722 ------15 fective ionic radius of about 0.52 angstrom, chromium 1.4614 ------20 (Cr3+) having an effective ionic radius of 0.62 angstrom, 1.3791 ------2 and rhodium (Rh3+) having an effective ionic radius of 1.3151 ------15 about 0.70 angstrom. The cations represented by B may, TABLE, 5 20 however, be any metal ion having a stable --3 formal valence and an effective ionic radius of from 0.50 to 1.05 X-ray powder diffraction pattern for palladium rhodium angstroms. Such metal ions include the Group IIIa metals, delafossite (PdRhO2) scandium, yttrium, and the lanthanides; titanium in Group d: I/IIo IVa; vanadium in Group Va; the Group VIa metals chro 6.0209 ------5 25 mium, molybdenum, and tungsten; the iron triol, iron, 3.0130 ------90 cobalt, and nickel; the second transition series platinum 2.5884 ------10 group metals ruthenium, rhodium, and palladium; the 2.5141 ------100 Group IIIb metals aluminum, gadolium, indium, and thal 2.2644 ------95 llium; tin and lead in Group IVb; and antimony and bis 2.1198 ------5 30 muth in Group Vb. 2.0088 ------2 The platinum delafossites include the stoichiometric 1.7104 ------85 oxycompound of platinum and cobalt having the delafos 1.5071 ------15 site structure (PtCoO) as well as non-stoichiometric oxy 1.4874 ------70 compounds of platinum and cobalt having the delafossite 1.5106 ------85 35 structure. Such non-stoichiometric delafossites have the 1.3503 ------80 formula: 1.2945 ------60 Finally to be noted is a medium intensity peak at from PtinCo nO2 about 1.6453 to about 1.7104 angstroms. This peak has S 1 — an intensity of from about 0.30 for palladium chromium 40 where in is between 0.5 and 0.8. delafossite to about 0.85 for the palladium cobalt Additionally, in the delafossites especially, the platinum (PdCoO) and palladium rhodium (PbRhO2) delafossite. delafossites, small amounts of other metal ions, such as It is at 1.6453 angstroms for the platinum cobalt (PtCoO2) scandium, titanium, vanadium, chromium, manganese, delafossite, at about 1.6445 angstroms for the palladium iron, cobalt, or nickel may be present. When such is the cobalt delafossite, at about 1.6864 angstroms for the pal case, the delafossite has the formula: ladium chromium delafossite, and at about 1.7104 ang PtxCoyMO2 stroms for the palladium rhodium delafossite. Delafossites include metal oxycompounds having the X-ray diffraction where x is from about 0.70 to 1.00, y is from about 0.70 patterns tabulated in Tables 1 through 5, inclusive, which to 1.00, and z is less than 0.11. Typically, z is from about data are pictorially represented in FIGS. I through V 0.004 to about 0.11, M is Sc, Ti, V, Cr, Mn, Fe, Co, or Ni. inclusive, and described hereinbefore. The platinum cobalt delafossite particularly useful as Chemically, delafossite oxides are oxycompounds of the electrode surface of this invention has a formula: two or more metals having the general formula: Pt4+nCo, nO2 ABO 5 5 2 3 While the general formula ABO2 is given, it should be where n is from about 0.50 to about 0.8. noted that non-stoichiometric compounds having defect The palladium delafossites particularly useful in pro structures are possible and are included within the scope viding an electrode surface of this invention are those of this invention. Such non-stoichiometric, defect struc delafossites having the formula: tured delafossites have the formula AxBy O2, where either 60 x or y or both are less than 1; for example, from about PdMO 70 to 1.00. Such delafossites are within the contemplated where M is cobalt, chromium, rhodium, ruthenium, lead, scope of this invention. When delafossites having the for or a lanthanide (including yttrium), or mixtures thereof. "mula ABO are referred to herein, such non-stoichiometric Such palladium delafossites, as palladium cobalt delafos delafossites are also contemplated. 65 site (PdCoO2), palladium chromium delafossite The metal ion represented by A may be any formally * monovalent metal ion having an effective ionic radius of (PdCrO2), from about 0.45 angstrom unit to about 0.68 angstrom palladium rhodium delafossite (PdRhO), the palladium unit. Such monovalent ions are copper (Cu+) with an delafossite of chromium and rhodium effective ionic radius of 0.47 angstrom, palladium (Pd+) 70 having an effective ionic radius of about 0.59 angstrom, (PdCrO2/PdRhO), platinum (Pt+) having an effective ionic radius of about the palladium delafossite of cobalt and rhodium 0.60 angstrom, and silver (Ag+) having an effective ionic radius of about 0.67 angstrom. Two, or more of such (PdCoO,/PdRhO), monovalent cations may be present in the same delafossite 75 the palladium delafossite of ruthenium (PdRuO), the

3,804,740 13 14 Thereafter the delafossite, synthetized by one of the hours, heated to a temperature of 110° C. for 1 hour, above methods, may either be utilized itself as an elec and thereafter sealed. The sealed quartz tube was heated trode or may be applied to a suitable electroconductive to a temperature of 850° C. for 15 minutes and then the base or substrate member to provide an electrode. temperature was decreased to 700° C. Heating continued Typically, as described hereinabove, the electrocon at about 700° C. for 65 hours. The resulting product was ductive base or substrate member will be a valve metal scraped from the quartz wall and ground carefully. It such as titanium. Such base or substrate member may be was thereafter leached twice with 200 milliliters of water in the form of a flat, plate-like sheet, or it may be in at 25° C., was washed with acetone, and dried. In this the form of a perforate sheet or expanded mesh. Alterna way 2.40 grams of a metallic gray-material were obtained. tively, it may be in the form of fine wires, rods, or other The material had particles in the size range of 0.03 to 0.5 shapes in order to allow the flow of evolved gases away 10 micron and 1 to 7 microns. from the volume between the anode and the cathode into This powder was examined by X-ray diffraction using spaces behind the anode. a Phillips diffractometer. The X-ray tube was operated When a titanium member is utilized as the base i or at 35 kv. and 15 milliamperes, and the detector was op substrate member, such titanium member is prepared for erated at 1265 volts. Radiation from a copper target was use as an electrode substrate by degreasing and etching used. The diffractometer was operated with a 1° diver prior to deposition of the delafossite surface. Degreas gence slit, a 0.006 inch receiving slit, and a 1° scatter slit. ing may be carried out by any of the methods well known The detector was rotated at 2° two theta per minute with in the art such as by the use of detergents, abrasives, a time constant of 2 seconds. The specimen was rotated or organic degreasing agents. Thereafter, the degreased at 1° per minute. The X-ray diffraction data shown in titanium base or substrate member may be etched in hy 20 Table 6 and FIG. VI were obtained. drofluoric acid, hydrochloric acid, or the like. The etch ing serves to remove the naturally-occurring oxide film TABLE 6 and substitute therefore a thin hydride film. , d: I/O The delafossite may be applied to the etched titanium 5.925 ------40 surface in a number of ways. For example, a slurry of 25 4.572 ------5 the delafossite may be prepared in a solvent such as eth 3.448 ------5 anol, butanol, benzyl alcohol, phenol, benzene, cumene, 2.957 ------90 or the like. Such slurry may be brushed onto the surface 2.566 ------10 of the titanium followed by heating to decompose or 2.440 ------60 volatilize the solvent after each coat. The slurry may 30 2.362 ------100 additionally contain a particulate compound I of silicon, 2.252 ------5 titanium, zirconium, hafnium, vanadium, niobium, tan 2.148 ------40 talum, molybdenum, tungsten, or other material capable 1.759 ------10 of forming an oxide in situ during the process of volatiliz 1.646 ------50 ing or decomposing the solvent. Most frequently, such 35 . . 1-480 ------10 particulate compound will be a chloride such as titanium 1.438 ------20 trichloride, TiCl3, or the like. 1.415 ------30 Alternatively, a slurry of the delafossite, a metal, and 1.350 ------5 an organic solvent such as ethanol, butanol, benzyl, alco 40 1325 ------5 hol, phenol, benzene, cumene, polyene, or the like, and a 1.277 ------20 silica compound or metal compound soluble or dispersi 1.273 ------20 ble in the organic solvent such as a resinate, may be pre A titanium coupon 534 - inches by 3% inch by 4/6 inch pared. Such slurry may be brushed onto the titanium . . was washed with Comet (TM), a household cleanser con providing, for example, from about 4 to about 8 coats 45 taining abrasives - and cleansers," rinsed in distilled water, with heating after each coat to decompose or volatilize and dipped in one weight percent hydrofluoric acid for 1 the organic constituent. Alternatively, methods such as minute. Thereafter the coupon was inserted in 12 normal compression bonding or cathodic electrophoresis may b hydrochloric acid at 27° C. for 23 hours. used to apply the coating of delafossite. . *** A solution was prepared - of 10 grams of Engelhard While the above described methods of coating the tita 50 “O-5X” Platinum Resinate (containing 7.5 weight per nium substrate with delafossite have described the use of cent platinum calculated as - the metal) and 9 grams of a titanium or silicon compound, such compound is not toluene. Three coats of this solution were applied to the necessary to the functioning of the i electrode. However, etched titanium - coupon. After each of the first two coats the oxidation product of such compound, that is, titanium the coupon was-heated at the rate of 50° C. per 5 minutes dioxide or silicon dioxide, does provide additional physical 55 . to 500° - C. and maintained thereat for 10 minutes. After strength and durability to the delafossite surface. Alterna the third-coat - the coupon was heated at the rate of 50° tively, oxides of zirconium, hafnium, vanadium, niobium, *C. per - 5 minutes to 550°. C." and maintained thereat for tantalum, molybdenum, or tungsten may be formed in 10 minutes. - - - - V . - - - W situ during the formation of the surface to provide a i A-slurry was prepared- of 0.5 gram of the palladium co durable electrode surface. -: - 60 g balt delafossite (PdCoO2), 1 gram of a 4.5-weight percent The resulting electrode prepared as described above titanium solution (prepared by adding 3.4 grams of ti may be utilized as an electrode for the conduct of elec tanium- trichloride, TiCl3 to 20 grams of ethanol), and trochemical reactions as hereinbefore described. . . 1.0 gram of ethanol. Six coats were brushed onto the The - following examples are illustrative. etched titanium. coupon. After each coat the coupon was EXAMPLE I 65 heated to 100° C. for 30 minutes. Thereafter, after the last coat, under, the pull of a vacuum pump, the coupon An electrode was prepared having a palladium cobalt was heated to 400° C. at a rate of 100° C. per 10 minutes, (PdCoO2) delafossite surface on a titanium substrate and held at 400º C. for 40 minutes. with an intermediate metallic platinum layer between the After the final coat the electrode was tested in a beaker titanium and the delafossite. 70 chlorate, cell. The beaker chlorate cell was a 500 milli The delafossite was prepared from 2.6642 grams of liter beaker having a platinized titanium cathode spaced palladium chloride (PdCl2) and 2.2482 grams of cobalt 38 inch from the anode by a Teflon (TM) spacer and con oxide. The chloride and oxide were thoroughly ground. taining a saturated solution of sodium chloride. The elec They were introduced into a 10 millimeter outside diame trolysis was conducted at a current density of 500 amperes ter 5-inch long quartz tube which was evacuated for 2 75 per square foot, and a cell voltage of 3.50 volts. The

3,804,704 19 20 porous titanium dioxide layer on the delafossite surface. as the metal, was prepared. Four coats of this slurry were The platinum-cobalt delafossite was prepared by the applied to the delafossite surface of the electrode. After reaction of platinum chloride (PtCl2) with cobalt (+-2, each of the first three coats, the electrode was heated to ----3) i oxide (Co3O4) and cobalt (--2) oxide (CoO). A 110° C. for 20 minutes, then to 425° C. for 10 minutes. minus 325 mesh powder was prepared containing 7.9842 After the fourth coat, the electrode was heated to 110° C. grams of platinum chloride (PtCl2), 3.6123 grams of co for 20 minutes and then to 500° C. for 15 minutes. balt (--2, --3) oxide (Co3O4), and 1.1241 grams of The resulting electrode, having a platinum-cobalt dela cobalt (--2) oxide (CoO). This powder was ground and fossite surface in a titanium substrate and a porous tita mixed with a mortar and pestle. The powder was placed nium dioxide exterior surface, was tested as an anode in in a 5 inch by 10 millimeter outside diameter quartz tube, | 0 a beaker chlorate cell as described in Example I herein heated at 130° C. under the pull of a vacuum for 18 hours, above. At a current density of 500 amperes per square and then sealed. foot, the anode voltage was 1.160 volts against a calomel The sealed quartz tube was heated for 46 hours at 700° electrode, and the chlorine overvoltage was 0.10 volt. C. The material was then removed from the quartz tube, The anode was then inserted in a laboratory diaphragm reground, and placed in another 5 inch by 10 millimeter 5 chlorine cell of the type described in Example I herein outside diameter quartz tube. The material was heated above. Electrolysis was conducted as described in Exam under the pull of a vacuum pump for 8 hours at 130° C., ple I hereinabove at a current density of 500 amperes per and then the tube was sealed. The tube containing the ma square foot. The initial cell voltage was 3.74 volts, and terial was heated to 700º C. for 64 hours. the initial chlorine overvoltage was 0.10 volt. After 74 The material was removed from the tube, leached five 20 days of electrolysis, the cell voltage was 3.94 volts and times with distilled water at 25° C., leached twice with the chlorine overvoltage was 0.17 volt. acetone at 25° C., and then dried in air at 70° C. The material was then ground to minus 325 mesh in a mortar EXAMPLE VIII and pestle. The resulting powder was then further ground An electrode was prepared having a platinum-cobalt for one hour in a “Mixer Mill” (TMI) by continuous 25 delafossite (Pto.Coo.O2) surface on a titanium base, impact with a boron carbide piston. with a ruthenium dioxide (RuO2) layer between the dela The resulting material was examined by a scanning elec fossite surface and the titanium base. tron microscope and found to have an overall size range A 534 inch by 3% inch by 2/8 inch titanium coupon was of 0.02 to 7.5 microns. The size range distribution was degreased, cleaned, and etched as described in Example I . bimodal, with the bulk of the material being from 0.02 to 30 hereinabove. A solution was prepared containing 1.5 grams 0.3 micron, and from 1.5 to 6.0 microns. The median size of ruthenium trichloride (RuCl3·3H2O), and 9 grams of of the fines was 0.10 micron, while the median size of the ethanol. Five coats of this solution were brushed onto the larger particles was 2.5 microns. coupon. After each of the first four coats the coupon was A 534 inch by %s inch by V6 inch titanium coupon was dried in air for 10 minutes and then heated in air to 300° cleaned and etched as described in Example I hereinabove. 35 C. for 10 minutes. After the last coat the coupon was A slurry was prepared containing 0.25 gram of the dried in air for 10 minutes and then heated in air to 450° PtoCoo.O delafossite prepared above, 0.12 gram of C. for 45 minutes. titanium tetrachloride, TiCl4 in butanol, 0.75 gram of A slurry was prepared containing 0.5 gram of the butanol, and 0.15 gram of phenol. Eight coats of the platinum cobalt delafossite (Pto.Coo.8O2) prepared in Ex slurry were applied to the titanium coupon. The coupon 40 ample VI hereinabove, 1.0 gram of a solution containing was heated after each coat to 425° C. at the rate of titanium tetrachloride (TiCl4) in butanol (having 4.2 50° C. per 5 minutes. weight percent titanium calculated as the metal), 0.2 gram Thereafter, a slurry of titanium tetrachloride (TiCl4) of phenol, and one drop of GAF “Igepal CO-530” nonyl in butanol was prepared, containing 2.25 weight percent phenoxy polyoxyethylene ethanol. titanium calculated as the metal. Four coats of this slurry 45 Six coats of the slurry were applied to the coupon. were applied to the delafossite surface of the coupon. After After each coat the coupon was heated at 110° C. for 20 each of coats 1, 2, and 3, the coupon was heated to 110° minutes; then to 400° C. for 15 minutes. Thereafter, the C. for 20 minutes and thence to 425° C. for 10 minutes. coupon was coated with a solution of titanium tetrachlo After the last coat the coupon was heated to 110° C. for ride (TiCl4) in butanol, containing 2.1 weight percent 20 minutes; thence to 500° C. for 15 minutes. 50 titanium calculated as the metal. One coat of the titanium In this way an electrode is provided having a platinum tetrachloride-butanol solution was applied, and the coupon cobalt delafossite surface on a titanium base with an eX was heated to 110° C. for 20 minutes; then to 500° C. for ternal titanium dioxide coating. The resulting electrode 15 minutes. By this procedure an electrode was obtained was inserted in a beaker chlorate cell and utilized as an having a uniform bluish-gray appearance. anode as described hereinabove. At a current density of The resulting electrode was tested as an anode in a 500 amperes per square foot the anode had an anode volt beaker chlorate cell following the procedure described in age of 1.175 volts versus a standard calomel electrode and Example I hereinabove. At a current density of 500 a chlorine overvoltage of 0.12 volt. amperes per square foot the anode had an anode voltage EXAMPLE VIII of 1.147 volts versus a standard calomel electrode, and a 60 chlorine overvoltage of 0.09 volt. An electrode was prepared having a platinum-cobalt The anode was then inserted in a laboratory diaphragm delafossite (Pto.Coo.O2) surface on a titanium substrate chlorine cell of the type described in Example I herein and an exterior TiO2 coating on the delafossite surface. above. Electrolysis was conducted as described in Exam A 534 inch by 3% inch by % inch titanium coupon ple I hereinabove at a current density of 500 amperes per was cleaned and etched as described in Example I here 65 square foot. The inital cell voltage was 3.60 volts and the inabove. A slurry was then prepared containing 0.5 gram initial chlorine overvoltage was 0.09 volt. After 936 hours of the platinum-cobalt delafossite (Pto.Coo.O2) prepared of electrolysis, the cell voltage was 3.72 volts and the in Example VI hereinabove, 0.25 gram of a solution con chlorine overvoltage was 0.07 volt. taining titanium tetrachloride (TiCl4) in butanol (having 4.5% titanium in titanium metal), 0.75 gram of butanol, 70 EXAMPLE IX and 0.15 gram of butanol. Six coats of the slurry were An anode was prepared having a palladium cobalt dela applied to the coupon. After each coat the coupon was fossite (PdCoO2) surface on a titanium base member heated to 110° C. for 30 minutes and then to 400° C. with an intermediate ruthenium dioxide (RuO2) coating for 15 minutes. A solution of titanium tetrachloride in between the base and the delafossite surface. butanol, containing 2, 1 weight perçent titanium calculated A 534 inch by 3% inch by V6 inch titanium coupon was