Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide

Definitions

• the invention relates to a porous high surface area composite electroconductive catalytic material particularly suitable for use in electrolytic processes as well as methods of producing this material and electrolysis electrodes comprising this material as electrocatalyst e.g. as an electrocatalytic coating.
• the invention also relates to the renewal of coatings on dimensionally stable electrolysis electrodes. It further relates to methods of electrolysis in which the reaction is catalyzed by this material e.g. the electrolytic production of halogens especially chlorine, hypochlorite and chlorate, metal electrowinning processes and so forth.
• OMP I A -- WIP stabilized without detriment to its catalytic characteristics.
• These coatings in particular ruthenium-titanium oxide coatings, have been especially successful in chlorine production in mercury cells, diaphragm cells and, more recently, in membrane cells.
• thermodecomposable compounds of the components are mixed in a solution which is repeatedly applied to the electrode substrate, dried and converted to the multicomponent coating by baking.
• thermodecomposable compounds of the components are mixed in a solution which is repeatedly applied to the electrode substrate, dried and converted to the multicomponent coating by baking.
• Multilayer elect-rode coatings produced by building up alternate layers of different materials have also been proposed.
• US Patent 3 773 554 describes alternat layers of ruthenium oxide and titanium oxide
• US Patent 3 869 312 describes alternate layers of a ruthenium-titanium mixed oxide material and of titanium oxide.
• Patent 4 331 528 made an important improvement in this area b developing a preformed barrier layer formed as a surface oxid film integral with and grown up from the valve metal substrat with simultaneous incorporation of a small quantity of rhodiu or iridium as metal or oxide in the surface oxide film, the active coating being subsequently deposited on top.
• Japanese Patent publication 028262/ provided an undercoating of an oxide of ruthenium, tin, iridi or rhodium on a valve metal substrate, and an active outer coating of palladium oxide or a mixture of palladium oxide an ruthenium oxide.
• Japanese Patent publication 115282/76 a spinel-type underlayer consisting preponderantly of Fe 2 ° 3 with other non-precious oxides was coated with a top-layer of precious metal oxides.
• US Patent 4 203 810 has proposed to electroplate a relatively thick layer of a platinum group metal onto an undercoat of a chemideposited platinum-group metal or oxide.
• the converse arrangement is described in published European patent application 0 090425, in which an oxide of ruthenium, palladium or iridium is chemideposited into a porous layer of platinum electroplated onto an electrically-conductive substrate.
• Other proposals for intermediate layers have included a underlayer of ruthenium, rhodium or pall r.
• electrocatalysts are generally coated onto a massive substrate such as a sheet of valve metal, one common configuration being an expanded mesh.
• the electrocatalyst can be particulate or can be supported on particles of suitable material such as a valve metal and these particles may then be applied to a conductive lead substrate (see US Patent 4425 217) or may be incorporated in a narrow gap electrolysis cell e.g. by bonding to a membrane as disclosed in European Patent Application 0 081 251, or they may be used in a fluidized bed electrochemical cell (see US Patent 4 206 020).
• Other substrat configurations include wires, tubes, perforated plates, reticulated structures and so forth.
• Electrodes with catalytic coatings of the types described above may be used in various electrolytic processes. Typicall they are used as anodes in chlor-aikali cells or as oxygen evolving anodes e.g. in metal electrowinning processes. Their use as cathodes in various processes has also been proposed, e.g. for the production of chlorine dioxide, as disclosed in
• OMPI WIPO European Patent Application 0 065 819 The latter patent application also proposed the same materials as heterogeneous catalysts for the non-electrochemical production of chlorine dioxide.
• Typical catalysts for this application included codeposited oxides of ruthenium/rhodium, ruthenium/rhodium/palladium and ruthenium/palladium usually codeposited with a matrix of titanium dioxide. The catalysts were usually deposited on a titanium substrate but other supports such as alumina were also proposed.
• European Patent Publication 0099 866 describes a catalys for the oxygen evolution reaction in water electrolysis.
• This catalyst comprises a host matrix of a transition element namel cobalt, nickel or manganese which incorporates one or more modifier elements deposited for example by vacuum sputtering and then subjected to a heat treatment or an.electrochemical treatment. Improved activity is claimed in relation to a nickel anode.
• porous high surface area electroconductive catalytic material comprising at least one platinum group metal and/or at least one platinum group metal oxide which is applied to a support, advantageously a porous pre-formed matrix e.g. of titanium oxide.
• a porous high surface area electroconductive catalytic material comprising a porous preformed catalytic matrix supporting a subsequently-applied additional catalyst.
• an economical anode coating with enhanced resistance to caustic for use in membrane cells.
• an - economical anode coating with high chlorine selectivity i.e. selective inhibition of oxygen evolution
• an anode coating with low oxygen overpotential and long life in sulphuric acid for metal electrowinning from sulphate solutions there is also a need for an anode coating with low oxygen overpotential and long life in sulphuric acid for metal electrowinning from sulphate solutions.
• mercury cell plants where operating conditions are particularl severe it would be desirable to improve the resistance of the anode coatings to contact with amalgam.
• the invention provides a porous high surface area composite electroconductive catalytic material comprising a porous pre-formed matrix throughout whic is dispersed at least one subsequently-applied platinum-group metal and/or at least one platinum-group metal oxide.
• the composite catalytic material has an outer face which in use is in contact with a fluid medium, typically an aqueous electrolyte;
• the porous matrix is a catalytic material comprising at least one platinum-group metal oxide and at least one non-precious metal oxide mixed intimately in a porous high surface area structure.
• the applied platinum group metal and/or oxide is carried by this structure as a thin, discontinuous layer whereby both (a) the platinum-group metal oxide of the preformed matrix and (b) the applied platinum group ir.etal and/or oxide which are disposed
• Such a thin layer of the subsequently-applied catalyst will typically be non-uniformly distributed in the matrix. Also, it may partly be integra.ed or diffused into the matrix.
• Another aspect of the invention is a porous high surface area composite electroconductive catalytic material comprising a porous preformed catalytic matrix and a subsequently-applied additional catalyst dispersed throughout and supported by the preformed matrix, wherein:
• the preformed matrix is a mixed catalytic material comprising at least one platinum-group metal oxide mixed intimately with at least one n ⁇ n-precious metal oxide in porous high surface area support structure, preferably as a mixed-crystal with the non-precious metal oxide present in an amount of at least 50 mol%;
• the subsequently-applied additional catalyst is a modifier catalyst which is of different composition to th mixed catalytic material of the preformed matrix, notably the additional catalyst is predominantly of catalytic material (usually, more than 90% by weight and preferably more than 95% by weight of catalytic material), and
• the subsequently-applied additional catalyst is carried by the preformed matrix as a thin discontinuous layer non-uniformly distributed in the porous high surfac area support structure whereby the mixed catalytic material of the preformed matrix located within the high surface area support structure is exposed through discontinuities of the subsequently-applied additional catalyst to external media.
• ruthenium-titanium oxide e.g. in a mol ratio of about 1:1 to 1:3, or even down to 1:10
• ruthenium-titanium-tin oxide e.g. in a mol ratio of about 1:2-5:0.5-1
• ruthenium-tin oxide e.g. in a mol ratio of about 1:2-5:0.5-1
• ruthenium-tin oxide e.g. in a mol ratio of about 1:2 to 1:9
• iridium-tantalum oxide e.g. in a mol ratio of about 1.9:1 to 5.5:1 and so forth.
• these mixed crystal materials will contain 10-50 and preferably 15-45 mol% of the platinum-group metal oxide(s) and the balance non-precious metal oxides.
• These mixed crystal materials are produced by codeposition of the components and form a single crystalline phase of rutile structure. However, the material may include minor or trace amounts of codeposited oxides finely dispersed in the mixed crystal material but forming a separate crystalline phase.
• Such separate codeposited oxides may be an excess of one of th components of the mixed crystal material, or may be a separate component such as a dopant.
• the porosity of codeposited mixed crystal materials is non-uniform and in practice these materials have a so-called mud-cracked appearance. It is this non-uniform porosity which provides the mixed crystal material with an exceptionally high surface area.
• the mixed crystal material of the porous matrix is a coating keyed to the surface of a valve metal base prior to incorporation of the applied platinum-group metal and/or oxide.
• valve metal is meant titanium, zirconium, niobium, tantalum and tungsten and, as far as the base is concerned, this term is also meant to cover alloys of these metals or of at least one of these metals with another metal o metals which when connected as anode in an electrolyte in whic the coated base is subsequently to operate as anode, there rapidly forms a passivating oxide film protecting the underlying metal from corrosion by the electrolyte.
• titanium will be the preferred base material.
• the porous matrix is formed by codepositing thermally decomposable platinum-group metal and non-precious metal compounds onto a valve metal base and baking in an oxidizing atmosphere to produce a porous coating preferably having a thickness corresponding to at least about 5g/ of the platinum group metal plus non-precious metal.
• the porous matrix consists of a used electrocatalytic coating of a dimensionally stable electrolysis electrode.
• the porous mixed crystal material is used as a high surface area host matrix to support a subsequently-added additional catalys in accordance with the claims, usually a thin layer of platinum-group metal and/or oxide. It is believed that the catalyst(s) of the mixed crystal material and the subsequently-applied additional catalyst(s) act as it were in tandem since the increase in performance is usually a multiple of the performance one would expect from the individual catalysts operating separately.
• rhodium oxide, palladium oxide, iridium oxide and platinum metal have all given very good results when added to a porous matrix based o ruthenium oxide, e.g. ruthenium-titanium oxide.
• the applied component comprises platinum re al and at least one oxide of rhodium, palladium and iridiu
• the applied component comprises at least two oxides of ruthenium, rhodium, palladium and iridium.
• the best results to date have been obtained with the following combinations on a ruthenium-titanium oxide matrix (or a ruthenium-tin oxide matrix) : rhodium-palladium oxides, rhodium-palladium-iridium oxides, rhodium-iridium oxides, ruthenium-rhodium oxides, palladium-iridium oxides, and ruthenium-palladium-iridium oxides.
• the four oxides may of course also be combined in various proportions.
• the additional catalyst i composed of rhodium-palladium oxides ranging from 95:5 to 5:95 weight% rhodium to palladium.
• Another- excellent additional catalyst combination is ruthenium-rhodium oxides having 10-40%. ruthenium and 60-90% rhodium by weight of the metals.
• the additional catalyst is composed of ruthenium-palladium-iridium oxides containing from 50-90% ruthenium, 5-25% palladium, and 5-25% iridium, all by weight of the metals. '
• Yet another advantageous combination of additional catalysts is rhodium-palladium-iridium oxides in the ratio 50-90% rhodium, 5-25% palladium and 5-25% iridium, all by weight of the metals.
• the additional catalyst will be valve-metal free and in any event the additional catalyst will consist of at least 90% and advantageously 95% or more by weight of catalytic materials, i.e., specifically excluding an significant amount of inert materials such .as valve metal oxides.
• the platinum-group metals and/or platinum group metal oxides it will in some instances be advantageous to incorporate non-precious catalytic material such as the oxides of cobalt, nickel, iron, lead, manganese an tin or tin/bismuth, tin/antimony in the subsequently-applied additional catalysts. Incorporation of these catalytic
• non-precious metal oxides in the additional catalyst is particularly advantageous when mixed or combined with at leas one platinum group metal and/or oxide.
• Another aspect of the invention consists of the composit catalytic material wherein the porous matrix is a catalytic mixed crystal material comprising at least one platinum-group metal oxide and at least one co-formed non-precious metal oxi forming a porous high surface area coating on a valve metal base, the subsequently-applied platinum group metal and/or oxide being dispersed in this structure by chemideposition fr an essentially non-precious metal free solution of at least o thermodecomposable platinum-group metal compound followed by annealing whereby both (a) the platinum-group metal oxide of the preformed matrix and (b) the applied platinum group metal and/or oxide disposed inside the structure are exposed throug the pores of the composite electrocatalytic material to the medium- contacting the outer face of the composite catalytic material.
• the porous matrix is a catalytic mixed crystal material comprising at least one platinum-group metal oxide and at least one co-formed non-precious metal oxi forming a porous high surface area coating on a valve
• the electroconductive catalytic materials described abov may be produced by:
• porous matrix which is a catalytic material comprising at least one platinum-group metal oxide and a least one non-precious metal oxide mixed intimately in a porous high surface area structure, preferably a mixed crystal material of rutile structure;
• porous matrix impregnating the porous matrix with either an essentiall non-precious metal free solution containing at least one thermodecomposable platinum-group metal compound or, mor broadly, a solution containing compounds which are decomposable to form a modified catalyst of different composition to the mixed catalytic material of the porou matrix, the modifier catalyst containing at least 90% by weight of a catalytic material;
• OMPI and heat treating the impregnated porous matrix to conver the compound(s) to at least one platinum-group metal and/or oxide or other modifier catalyst dispersed throughout the porous matrix.
• the heat treatment may take place in an oxidizing atmosphere such as air or in controlled non-oxidizing or partially oxidizing conditions i.e. in a reducing, inert or mildly oxidizing atmosphere such an ammonia-air mixture or a nitrogen-hydrogen mixture.
• a reducing agent may also be included in the solution.
• Each applied coat is subjected to a short heat treatment to convert the compound(s) to the metal and/or oxide and after application of the final coat the heat treatment is preferably completed by annealing in air at a temperature of from 300 to 600°C for up to 100 hours. • Excellent results have been obtained with such a post heat treatment at 450-550°C for from 2-30 hours.
• this post heat treatment ha been found to provide a remarkable increase in performance. This is sometimes linked with baking in non-oxidizing or partial oxidizing conditions whereby the additional catalyst i initially formed as a metal or a partly oxidized metal, especially for additional catalysts including palladium.
• the post heat treatment in air serves to oxidize or to complete oxidation of the additional catalyst.
• the post heat treatment is also beneficial when the additional catalyst is initially formed in oxidizing conditions and may already be completely oxidized.
• the post heat treatment has an annealing effect which in some instances is associated with a distribution or equalization of the additional catalyst in the matrix.
• OMPI post heat treatment there may be a pronounced non-uniform distribution of the additional catalyst with greater density the auxiliary catalyst near the surface.
• the additional catalyst is more uniformly distributed (but rarely entirely uniformly distributed) in th matrix. Therefore, one of the characteristics of most composite catalytic materials of the invention is a non-unifo distribution of the additional catalyst throughout the thickness of the material.
• th method of the invention may comprise first forming porous matrix particles of an electrocatalytic mixed crystal materia of at least one platinum group metal oxide and at least one non-precious metal oxide for example by spraying a solution o thermodecomposable compounds of the components into air heate to about 400-500°C in a conventional spray drying apparatus, or alternatively using coprecipitation techniques.
• the matrix particles are then mixed into a solution of thermodecomposable compounds of the auxiliary catalysts, drie in a conventional particle drying apparatus and heated in air or a reducing atmosphere, optionally followed by a prolonged heat treatment as outlined above.
• support particles of various materials such as film-forming metals ca be coated with an electrocatalytic mixed crystal material of platinum group metal oxide and at least one non-precious meta oxide forming a porous matrix for a subsequently added cataly for example one or more of the oxides of ruthenium, rhodium, palladium and iridium.
• These catalytic particles and in particular those with favourable properties for oxygen evolution from acid electrolytes, may then for example be pressed into a supporting lead substrate as disclosed in U.S. Patent 4425 217.
• they may be incorporated in narrow gap electrolysis cell e.g. by bonding to a membrane, a disclosed in European Patent Publication 0 081 251.
• a further aspect of the invention is a catalytic electrolysis electrode comprising as electrocatalyst the catalytic material as set out above and in the claims or as produced by the methods as set out above and in the claims.
• the invention also pertains to a method of renewing a use coating of a dimensionally stable electrolysis electrode havin a valve metal base and a porous electrocatalytic coating comprising at least one oxide of a platinum-group metal and at least one non-precious metal oxide without recoating the electrode with a similar new coating.
• This method comprises impregnating the porous used coating with an essentially non-precious metal free solution containing at least one thermodecomposable platinum-group metal compound. The impregnated porous coating is then heated to convert the compound(s) to at least one platinum-group metal .and/or oxide- dispersed throughout the porous coating.
• comprising at least one oxide of a platinum-group metal and at least one non-precious metal oxide comprises impregnating the porous used coating with an essentially non-precious metal fre solution containing at least one thermodecomposable platinum-group metal compound and heat treating the impregnate porous coating in a non-oxidizing or partially oxidizing atmosphere followed by annealing in air at a temperature of from 300 to 600°C for up to 100 hours to convert the compound(s) to at least one platinum-group metal and/or oxide dispersed throughout the porous coating.
• the electrode with the thus activated coating can then be used for electrolysis, or it is possible to apply on top a new coating of similar composition to the old one, as taught in US Patent 4 446 245.
• Such methods of renewal find particular advantage when it is decided to convert a chlor-alkali diaphragm cell to the ion-exchange membrane process.
• the invention also pertains to a method of electrolysis wherein electrolysis current is passed between electrodes in an electrolyte, at least one of the electrodes including a porous catalyst having an outer face in contact with the electrolyte, wherein the catalyst is the catalytic material as set out above and in the claims or as produced by the methods set out above and in the claims.
• a particularly advantageous application of the invention is the production of chlorine/caustic in an ion-exchange membrane cell using anodes having catalytic coatings produced by renewing or converting the coatings of diaphragm-cell anodes as set out above.
• Titanium coupons measuring approximately 20 x 100 x 1.5 m were degreased, rinsed in water, dried, etched for 6 hours in 10% oxalic acid at 95°C, and then washed in water. They were then coated with a solution of 6 ml n-propanol, 0.4 ml HC1 (concentrated), 3.2 ml butyl titanate and 1 g RuClg. In all, five coats were applied, each coat being heated in air at 500°C for ten minutes. This produced electrodes with a ruthenium-titanium oxide mixed crystal coating in an approximately 30/70 mol ratio and containing approximately 8 q/vtt of ruthenium. The mixed crystal coating had porous mud-cracked configuration and was used as host matrix for additional catalysts as follows.
• the porous mixed crystal coatings were impregnated with a ⁇ JRE OMP solution containing various quantities of rhodium chloride and/or palladium chloride in 10ml isopropyl alcohol, 0.4ml HC1 (37%) and 10ml of linalool.
• Four applications were made and after each impregnation the electrodes were heated in an ammonia-air mixture (or, in the case of electrodes #53 and #31 in a nitrogen-hydrogen mixture or in air) at 500°C for ten minutes. Then the electrodes were submitted to a final heat treatment in air for 20 hours at 500°C.
• the electrodes were subjected to accelerated lifetime tests (a) in 180g/l H j SO ⁇ without external heating i.e. at about 30 C and at an anode current density of 15 kA/m and (b) in 30% NaOH at 95-96°C and at an anode current density of 28 kA/m .
• the electrode lifetimes under current reversal conditions were measured at an anode current density of 20 kA/ (a) in 180 g/l H-SO. at 30°C and (b) 25% NaCl at 80°C and pH 3-4. All of these lifetimes are given in hours in the Tables.
• the half-cell potentials for oxygen and chlorine evolutio were measured at an anode current density of 5 kA/m 2 in 180 g/l H 2 S0 4 and in 25% NaCl of pH 2-3, both at 80 C.
• the measured values were related to a normal hydrogen electrode (NHE) and are reported in Table 1 in millivolts. These values have not been corrected for ohmic drop.
• the acid lifetime was increased to 316 hours.
• the reducing agent linalool was omitted from the activating ⁇ -" ⁇ solution and the overall performance of the electrode improve marginally over sample #1.
• linalool was also omitted and conversion of the Rh/Pd solution was done in air instead of in air/ammonia.
• the resulting electrode had a poo acid lifetime.
• conversion was carried out in air instead of air/ammonia. In this case, the accelerated ac lifetime was 112 hours.
• Samples #11, #12 and #14 were subjected to post heat treatments in air at 500°C for different durations. Sample #11 with a 3 hour treatment demonstrates quite good performance. Sample #14 with a 90 hour treatment has an excellent lifetime in the accelerated acid test.
• the subsequently-applied additional catalyst of sample #58 consisted of codeposited rhodium/palladium/titanium oxide containing 1.5g Rh, 3.5g Pd and 0.5g Ti, obtained by includin butyl titanate in the solution. This considerably decreased the acid lifetime and increased the oxygen-evolution potentia compared to #1. The lifetime in the current reverse test in brine was good.
• #C1, #C2, #C3 and #C4 are comparative electrodes.
• the electrode coating consisted solely of the ruthenium-titanium oxide material in an amount corresponding 35 13g/m of Ru, i.e. the same total precious metal loading as in #1. The results shown are for an electrode without the
• comparative electrode #C2 consisted solel of rhodium-palladium oxide deposited on the titanium substrate under the same conditions but without the ruthenium-titanium oxide matrix. Again, for the purposes of comparison, the precious metal loading was 13g/m (3.9g Rh and 9.1g Pd).
• the accelerated lifetime in the acid test was meager 1.75 hours. This lifetime was increased to 6 hours by baking in air instead of ammonia-air.
• Comparative electrode #C3 likewise had a coating deposited directly on the titanium substrate without the ruthenium-titanium oxide matrix.
• This coating was composed of palladium-rhodium-titanium oxide in a mol ratio palladium-rhodium oxide : titanium oxide of 30:70 and was codeposited from a mixed solution.
• the coating contained 3.9g Rh and 9.1g Pd.
• the lifetime in the accelerated acid test was only 4 hours and the oxygen and chlorine evolution potentials were very high.
• Comparative electrode #C4 had a coating produced from a solution in which all of the four components (Ru/Rh/Pd/Ti) were mixed, each metal in the codeposited multicomponent coating being present in a corresponding amount to the same metals in the matrix and in the additional catalyst of #1.
• the baking necessarily had to be in air. Attempts were made to produce the mixed-solution multicomponent coating in a reducing atmosphere, but no adherent coating could be obtained.
• the resulting electrode is an improvement over the standard electrode #C1 but the improvement is largely offset by increased cost. Furthermore, inconsistent results have been obtained with these multicomponent coatings from mixed solutions. Some good results have been obtained but are difficult to reproduce.
• the electrodes according to the invention all have a lifetime in caustic which is a multiple of that of the prior art reference electrode #C1, e.g thirteen times as long for electrodes #5 (Table 1) and #8 (Table 2).
• caustic e.g. NaOH
• a further electrode was prepared with the same quantity of subsequently-applied additional catalyst (4g Rh and lg Pd) as sample #6 of Example 1 but incorporated in a matrix of ruthenium-tin oxide.
• This porous matrix was prepared in the same manner as the matrix of Example 1 but using a solution o 9.2ml n-propanol, 0.4ml HC1 (concentrated), 2.02g SnCl, and lg RuCl 3 .
• a well performing electrode was obtained having lifetimes of 192 hours and 96 hours in the accelerated acid a caustic tests. Lifetimes in the current reverse tests were 2. hours in acid and 5.5 hours in brine.
• the half-cell potential were 1580mV for oxygen evolution and 1310mV for chlorine evolution. The overall performance was therefore good, but n as good as the corresponding sample #6 with the ruthenium-titanium oxide matrix.
• Example 3 Further electrodes were prepared in the same manner as Example 1 but varying the additional catalyst combinations. These electrodes were subjected to the same tests and the results are shown in Table 3.
• Sample #17 illustrates the role of ruthenium as a diluent for the palladium catalyst.
• the performance of this electrode is comparable to sample #54 of Table 1 which contained 5g of palladium.
• sample #17 has a low oxygen evolution potential of 1490mV making this electrode advantageous for oxygen-evolving applications.
• Sample #28 shows a similar effect of ruthenium as diluent for rhodium (compare with sample #27 of Table 1) but in this case the lifetime in the accelerated acid test is increased by 100 hours to the excellent value of
• Sample #24 is particularly remarkable in view of the fact that the auxiliary catalyst consists predominantly (80%) of ruthenium with only modest amounts of palladium and iridium.
• Sample #33 in which the auxiliary catalyst is platinum/rhodium oxide has good all-round performance and very good performance in the current reverse test in brine.
• Sample #5P (which was produced with baking in air instead of ammonia air) is extraordinary in that it combines the long acid lifetime of Ir0 2 /Pt with a relatively low oxygen evolution potential (100-150mV below that of Ir0 2 /Pt alone, depending on the baking conditions of the Ir0 2 /Pt coating). It also has a very good lifetime in the current reverse test in H-S0 4 .
• Sample #22P is also extraordinary in that, compared to a corresponding electrode coated with 5g of ' platinum (i.e. without the matrix), it has a much longer lifetime and an oxygen evolution potential which is
• a titanium-based electrode was prepared with a
• the additional catalyst was deposited from a solution containing approximately O.lg iridium chloride, 6ml butanol and 0.4ml HC1
• Such an electrode is therefore more expensive in terms of its catalyst cost and also has a substantially greater manufacturing cost.
• Titanium sponge particles were degreased in a 50/50vol% mixture of acetone and carbon tetrachloride. The particles were then mixed with a solution of 15.6ml propyl alcohol, 0.4ml HC1 (concentrated), 3.2ml butyl titanate and lg RuCl 3 .H 2 0(40% Ru) in a ratio of lg of the particles for 0.5 ml of the solution. The sponge particles were then dried by heating in air in three stages, at 80°C, 150°C and 250°C and, after drying, heat treated in air at 500°C for 15 minutes.
• This surface-activated sponge may then for example be pressed into a lead substrate as disclosed in
• Titanium sponge particles were coated with a ruthenium-titanium oxide porous matrix which was impregnated with an iridium oxide additional catalyst in a similar manner to the procedure of Example 6 except that the baking was in air and there was no post heating.
• Various catalyst loadings were provided and comparative coatings without the iridium oxide additional catalyst were also provided as shown in Table 4.
• the particles were then pressed into a lead substrate as disclosed in US Patent 4425 217 and the catalyzed lead electrodes were subjected to an accelerated lifetime test as oxygen evolving anodes in 150g/l ⁇ -USO. at 50°C.
• the lifetimes given in Table 4 are in days on line (DOL).
• a titanium mesh pickled in hot hydrochloric acid for 1 hour was rinsed with water, dried in air and coated with a solution of 6.2ml butyl alcohol, 0.4ml HC1 36%, 3ml butyl titanate, and lg RuCl, H-0 (40% Ru).
• the porous mixed crystal coating (Ru0 2 .Ti0 2 ) is impregnated with a rhodium and palladium chloride containing solution as described in Example 1 and submitted to the same heat treatment so as to disperse throughout the ruthenium-titanium dioxide matrix a rhodium oxide and palladium oxide phase in an amount corresponding to 4g/m of Rh and lg/m of Pd.
• the resulting anode coating has outstanding performance as compared with standard mixed metal oxide coatings in membrane electrolyzers, with high resistance to caustic brine, improved selectivity for chlorine evolution (inhibition of unwanted oxygen) and high corrosion resistance.

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• 1984
  • 1984-09-13 EP EP84810446A patent/EP0174413A1/en not_active Withdrawn
  • 1984-09-17 JP JP59503512A patent/JPS62500459A/ja active Pending
  • 1984-09-17 BR BR8407356A patent/BR8407356A/pt unknown
  • 1984-09-17 WO PCT/EP1984/000285 patent/WO1986001839A1/en active Application Filing
  • 1984-09-17 KR KR860700269A patent/KR860700273A/ko not_active Application Discontinuation
• 1986
  • 1986-05-16 NO NO861978A patent/NO861978L/no unknown
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