Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/60—Deposition of organic layers from vapour phase
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/50—Processes
  • C25B1/55—Photoelectrolysis
• • 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
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound

Definitions

• the invention generally relates to semi-conducting N.-chelate coatings and their manufacture on electrically conducting substrates suitable for producing industrial electrodes of different types.
• Monomeric and polymeric phthalocyanines exhibit interesting electronic, electrocatalytic and photo-electrochemical properties.
• Naraba et al Japanese . Journal of Applied Physics, Vol. ⁇ (12) 977-986, describe the preparation of a poly-tetracyanoethylene chelate film. This work relates primarily to Cu and reports a film thickness of 1mm, with a significant Cu gradient across the film. This publication describes applying a vacuum of 10 " mm Hg and using high frequency heating to get a clean surface; such a procedure is hardly suitable for an industrial process.
• Polymeric phthalocyanines can exhibit high electrical conductivities which may be greater by ten orders of magnitude than the conductivities of monomeric phthalocyanines. They may have semi-conducting properties of the n or p type, depending on the conditions of preparation.
• N .-chelates and more particularly metal phthalocyanines were found to exhibit interesting catalytic properties for oxygen reduction in fuel cells where acid electrolytes are used to avoid carbonate formation.
• Polymeric phthalocyanines of high molecular weight are resistant to attack by acid media and exhibit high catalytic activity for oxygen reduction.
• N ⁇ -chelates present, their manufacture so as to provide useful industrial products is particularly difficult to achieve in a reproducible manner.
• the manufacture of electrodes consisting of N ⁇ -chelates has thus not been successfully achieved until now due to the problems of manufacturing satisfactory N ⁇ -chelates under controlled conditions on an industrial scale.
• N.-chelates as a coating material on a suitable electrically conducting substrate can provide electrodes of different shapes. However, in that case the electrode properties will also depend on the substrate material.
• a chelate coating must moreover meet the requirement of satisfactory adherence to the underlying electrode body providing a coating substrate. Chelates with different central metal atoms can provide different catalytic properties and the selection of chelates for use as electrocatalytic materials must be made according to the intended use in each case.
• An object of the invention is to provide stable, substantially uniform semi-conducting coatings formed of N ⁇ -eh elates bonded to conductive substrates, so as to meet as far as possible all technical requirements with regard to reproducibility, stability and conductivity.
• Another object of the invention is to provide electrodes with such chelate coatings wherein a controlled amount of a suitable chelating metal is distributed as evenly as possible throughout the coating.
• a further object is to provide such N.-chelate coatings which are substantially stable and insoluble in acid and alkaline media.
• the invention more particularly has the object of providing a manufacturing process for the industrial production of such highly stable conducting N ⁇ -chelate coatings with reproducible properties suitable for various technical applications.
• the invention provides a manufacturing process as set forth in the claims and as described in the examples given further on.
• the expression metal coordination centres as used herein with reference to the invention is meant to cover metal in the metallic state, as well as in any other form suitable for providing central metal ions attached by coordinate links to the iigands of the N ⁇ -chelate network.
• the process of the invention essentially provides controlled manufacturing conditions for the synthesis of an N ⁇ -chelate coating of predetermined, limited
• ⁇ 5 thickness formed in situ on the substrate surface by controlled heterogeneous reaction with a tetranitrile compound in the vapour phase, as well as for its subsequent conversion by controlled thermal treatment to a substantially uniform, stable polychelate coating having satisfactory, reproducible properties suitable for various technical applications.
• the process of the invention is thus more particularly intended to substantially control the various factors which can ensure the desired physical and chemical properties of the polychelate coating, while eliminating as far as possible all uncontrolled side effects which could affect the reproducibility of these coating properties.
• the process of the invention may be advantageously carried out as described further below in the examples, by effecting the controlled chelating reaction with a tetranitrile compound forming the vapour phase, without any additional gaseous components which might lead to uncontrolled side, effects and undesirable properties of the
• the chelating reaction is carried out in the process of the invention at a controlled temperature lying within the range of thermal stability, i.e. below the thermal decomposition temperature, of the tetranitrile compound used to manufacture the polychelate coating in each case.
• the amount (X ) of tetranitrile compound which is brought into the vapour phase, per unit substrate surface area available for the chelating reaction, is also carefully controlled, s as to restrict accordingly the specific amount (X) of chelate produced per uni area.
• the thickness of the resulting chelate coating is thus restricted i accordance with the invention, by limiting the specific amount (X ) o tetranitrile compound brought into the vapour phase, in order to thereby mak available only such a limited amount of this gaseous reactant as can b effectively chela ted throughout the entire coating on the substrate surface, an to thereby provide a substantially uniform chelate coating with reproducibl properties.
• the yield of the chelate formed on the substrate may vary considerably and wil depend on various parameters such as reaction temperature, specific amoun (X ) of reactant available per unit substrate surface area, and type o pretreatment of the substrate surface.
• the chelate yield will moreover depend on the design of the reacto used for the chelating reaction, as well as its dimensions relative to th substrate surface.
• a small reaction vessel was used in said experimental program whic showed that stable , adherent polychelate coatings may be obtained in accordanc with the invention under different operating conditions.
• the specifi amount (X ) of tetranitrile compound available in the vapour phase per uni surface area was varied from about 1 g/m 2 to 20 g/m 2 , the temperature fro
• the substrate surfac was moreover pretreated by sandblasting, etching with an acid or base, an polishing.
• tetracyanobenzene tetracyanoethyiene
• TCNE tetracyanoethyiene
• iron 0.5 6C
• stainless steel AISI 316L
• nickel titanium and graphite plate substrate samples.
• the following tetranitrile compounds were successfully used to manufacture polychelate coatings on titanium plates and other sheet substrates in accordance with the present invention: tetracyanobenzene tetracyanoethyiene tetracyanopyrazine tetracyanothiopene 0 tetracyanodiphenyl tetracyanodiphenyl ether tetracyanodiphenyl sulfone tetracyanofurane tetracyanonaphthalene -5 tetracyanopyridine.
• the metals which used to produce a polychelate coating in accordance with the invention may form the entire substrate body or be disposed at its surface to provide the metal coordination centres for the chelating reaction.
• other base metals such as for example cobalt, iron, nickel, aluminium and copper may also be used, either alone or in any suitable combination, for example with titanium or other valve metal mentioned above.
• Noble metals such as the platinum-group metals ⁇ aay also be used to provide suitable metal coordination centres, as well as any other purpose, for example to -5 provide catalytic properties and/or increase the substrate stability.
• metals which may be suitable for the invention can be combined in different ways, for example as an alloy which either forms the entire substrate body or only covers the substrate surface. ..
• the substrate body may also have any suitable size or shape such as, for example a plate, grid or rod.
• the substrate body may, moreover, have a porous surface for carrying out the chelating reaction.
• the substrate surface area available for carrying out the controlled chelating reaction in accordance with the invention may be advantageously increased as far as possible so as to increase accordingly the total reaction surface thus made available with respect to the projected area of the substrate body.
• Such an increase of the specific surface area available for the chelating reaction per unit projected area of the substrate is of particular significance for providing a corresponding increase of the metal coordination sites which are made available for chelation. An adequate number of metal coordination sites can thereby be ensured for manufacturing a substantially uniform, stable polychelate coating of desired thickness in accordance with the invention.
• thermal pretreatment of the substrate body under vacuum was found to provide significant improvements of the electrical properties of polychelate coatings produced in accordance with the invention.
• a substantially pure, uniform polychelate coating of - desired, predetermined thickness can be manufactured in a highly reproducible manner by bringing a predetermined specific amount (X ) of any suitable substantially pure tetranitrile compound into a vapour phase which does not contain any impurities that could affect the chelating reaction and by carefully controlling the temperature and duration of the chelating reaction and the thermal treatment so as to produce a uniform polychelate coating with reproducible properties.
• Said specific amount (X ) of the tetranitrile compound which is brought into the vapour phase may be selected within given ranges which may generally depend more or less on this compound, the substrate used and the reaction temperature.
• TCB tetracyanobenzene
• Sandblasting was found to be the most advantageous surfac pretreatment for iron, stainless steel and nickel.
• Such a catalyst may be added to further reduce the temperature which may be necessary in the case of substrates having lower melting points.
• the controlled thermal treatment carried out according to the invention essentially provides cross-linking and conversion to a substantially uniform, insoluble polychelate coating of high molecular weight.
• This thermal treatment may be advantageously carried out together with the chelating reaction as described more fully. However, it may also be carried out in a subsequent separate step under controlled conditions which may be different.
• the polychelate coating may also be manufactured in several successive steps, according to the invention, so as to gradually build up a thicker coating (e.g. above 10 microns) composed of several layers. In that case, additional metal centres .may be applied to each layer in any suitable way or by codeposition with the tetranitrile compound from the vapour phase.
• a thicker coating e.g. above 10 microns
• additional metal centres may be applied to each layer in any suitable way or by codeposition with the tetranitrile compound from the vapour phase.
• polychelate coatings according to the invention may be incorporated in the polychelate coatings according to the invention in order to provide "mixed" chelates and to thereby combine useful (complementary) properties of different chelating metals.
• the polychelate coating according to the invention may also be used advantageously as an undercoating for an outer electrocatalytic coating of any suitable type.
• the polychelate coating may also be manufactured according to the invention from a tetranitrile compound present in an inert atmosphere to prevent oxidation and contamination of the polychelate.
• Th e present invention further provides a chelate-coated electrode as set forth in the claims, with a substrate which comprises a valve metal such as • titanium, and may form an electrode base or support body, as described more fully in the examples. •5
• a valve metal such as • titanium
• Titanium sheet samples with a surface area of 2 cm were mechanically polished and then provided with a polychelate coating.
• This 10 coating was produced by placing each pretreated polished sample, together with a predetermined specific amount (X ) of tetracyanobenzene (TCB) in a vessel of heat resistant glass, which was then evacuated to a vacuum of about 10 " Torr, sealed, and heated at 400°C for 24 hours.
• X tetracyanobenzene
• Polychelate coatings were respectively produced on three 1* mechanically polished samples, but with different specific amounts (X ) of TCB corresponding respectively to 0.5, 1 and 8 mg TCB/cm of the sample surface. A uniform, adherent polychelate was thus obtained on each of these three samples.
• the three resulting coated samples were tested in an electrochemical cell by effecting cyclic voltametric measurements in a INK-SO ⁇ aqueous 20 solution containing a 1 mM ferri/ferrocyanide redox couple. These measurements were effected in the voltage range +0.85 V to +0.1 V vs. NHE
• a titanium sheet sample with a surface area of 2 cm was mechanically polished and further pretreated in a vessel which was evacuated to a vacuum of about 10 " Torr, sealed, heated at 400°C for 24 hours, and finally 0 cooled to room temperature.
• the polished titanium sample thus pretreated under vacuum was then provided with a polychelate coating obtained from TCB in an amount X corresponding to 0.5 mg/cm in a reactor vessel which was evacuated to a vacuum of about 10 -3 Torr, sealed and heated at 400 o C for 5 hours, as already -5 described in Example 1.
• the resulting coated sample thus obtained had a uniform, adherent polychelate coating and was tested under the same conditions already described in the preceding Example 1.
• a titanium sheet sample pretreated and coated as described in Example 2 was subjected to a test to determine its photo lectrochemical behaviour.
• the coated sample was immersed in a sulphate solution at
• a titanium sheet sample with a surface area of 2 cm was mechanically polished and provided with a polychelate coating produced from
• TCNE tetracyanoethyiene
• a titanium sample with a surface area of 2 cm was mechanically polished and provided with a polychelate coating produced from tetracyano- thiophene, under the same conditions as in Example 2.
• the coated sample thus obtained was also tested by cyclic voltametric measurements under the same conditions as already described in Example 1.
• the anodic and cathodic peak current densities were also tested by cyclic voltametric measurements under the same conditions as already described in Example 1. In this case, the anodic and cathodic peak current densities
• a titanium sheet sample with a surface area of 15 cm was first subjected to surface treatment by sandblasting and etching in oxalic acid for 6h.
• a polychelate coating formed from tetracyanoethyiene (TCNE) was applied by placing the pretreated titanium sample, together with 15 mg TCNE, in a vessel of heat resistant glass, which was then evacuated to a vacuum of about
• the coating showed excellent chemical resistance in H-SO ⁇ .
• a titanium sheet sample with a surface area of 15 cm 2 was first subjected to surface treatment by sandblasting and etching in oxalic acid for 6 hours.
• a polychelate coating formed from tetracyanoethyiene (TCNE) was 1-5 then applied by placing the pretreated titanium sample, together with 15 mg
• the resulting polychelate coating was then topcoated with a catalytic outer coating of tantalum-iridium oxide.
• This topcoating was formed by successively applying 4 layers of a solution comprising tantalum chloride and iridium chloride in alcohol (ethylalcohol and isopropylalcohol) in amounts
• a titanium sample was pretreated and provided with a polychelate coating in the manner already described in the preceding Example 7.
• This coated test sample had an initial anode potential of 1.44
• V/NHE V/NHE and operated for 360 hours in this current reversal test under the described conditions.
• a polychelate was then formed on the pretreated iron sample by placing it together with 8 mg of tetracyanoethyiene (TCNE) in a reaction vessel
• the coating shows good chemical resistance in 15% H 2 SO ⁇ .
• the initial amount of TCNE v/as increased to 15 and 30 mg.
• reaction temperature was shown by running comparative tests with an initial TCNE amount of 5.0 and 10 g/m at 400 C, 500 C and 600°C. A considerable increase in the specific coating weight can be observed by increasing the reaction temperature from 400 to 500 C while maintaining the reaction duration at 24h. This was particularly critical for obtaining sufficient chemical resistance in very corrosive media such as H ⁇ SO ft . Upon further increase of temperature to 600 C the amount of polychelate corresponds to 3.9 as shown above.
• the pretreatment and process conditions were identical to those applied to iron sheet samples.
• a sheet sample of stainless steel (AISI 316L; 50 x 15 x 1 mm) with a
• a polychelate coating was then formed on the pretreated steel sample by placing it together with 8 mg of tetracyanoethyiene (TCNE) in a reaction vessel of heat resistant glass, which was . evacuated to a vacuum of about 10 " Torr, sealed and heated at 550 C for 12 hours. A uniform polychelate coating firmly adhering to the steel plate was thus obtained.
• TCNE tetracyanoethyiene
• This coated sample was tested as an oxygen evolving anode operating at a current density of 4500 A/m in an electrolysis cell containing an aqueous NaOH solution with a concentration of 300 g/1. This test sample had an initial
• a sheet sample of stainless steel (AISI 316L) with a surface area of 2 15 cm was pretreated by sandblasting and precoated with a polymeric layer containing platinum.
• This precoating was obtained by successively applying 8 layers of a solution of polyacrylonitrile (PAN) and platinum chloride in dimethylformamide (DMF). After applying each layer of solution, it was dried and thermally treated for 10 minutes at 250°C in static air. After applying and heat treating each of the 8 layers, a further heat treatment was carried out for
• a polychelate coating was then formed by placing the pretreated sample, together with 30 mg tetracyanoethyiene (TCNE), in a glass vessel which was then evacuated to about 10 " Torr, sealed and heated at 600°C for 24 hours.
• TCNE tetracyanoethyiene
• This coated sample was tested as a hydrogen evolving cathode operating at a current density of 4500 A/m in an electrolysis cell containing an aqueous solution of NaOH at a concentration of 135 g/1 and at a temperature of
• a nickel sheet sample (99% Ni; 50 x 15 x 1 mm) with a surface area 2 of 15 cm was pretreated by sandblasting (with SiO-J-and degreasing with carbon tetrachloride in an ultrasonic cleaner.
• a polychelate coating was next produced by placing the pretreated nickel sample, together with tetracyanoethyiene (TCNE) in a specific amount X
• This coated sample was tested as a hydrogen evolving cathode
• the coated test sample was inspected by microscope after having operated for 3 months under the described conditions. No trace of deterioration of the coating was detected by microscope -after this operating period of 3 months.
• a sheet sample of nickel with a surface area of 15 cm was pretreated by sandblasting and degreasing.
• a polychelate 'coating formed from tetracyanoethyiene (TCNE) was applied by placing the pretreated nickel sample together with 15 mg TCNE in a vessel of heat resistant glass, which was then evacuated to a vacuum of about io " Torr, sealed, heated to 550°C and maintained for 24 hours at this temperature.
• the resulting coated sample was covered with a very uniform, adherent nickel-poly phthalocyanine coating with a thickness of 1.5/1.
• the chelate coatings manufactured in situ on a substrate body in accordance with the invention may be advantageously used for various appli ⁇ cations where stable, semi-conducting chelate coatings may provide technical or economic advantages, more especially to provide electrodes of different types, such as catalytic electrodes.
• a substrate body provided with a chelate coating according to the invention may either be used as such or further provided with an additional outer coating for any desired purpose such as a catalytic outer coating suitable for carrying out various technical processes.

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• 1981
  • 1981-02-06 CA CA000370266A patent/CA1185149A/en not_active Expired
  • 1981-02-23 US US06/315,852 patent/US4448803A/en not_active Expired - Fee Related
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  • 1981-02-23 WO PCT/US1981/000217 patent/WO1981002432A1/en not_active Ceased
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