Title of Invention

A PROCESS FOR MANUFACTURING AN ELECTRODE

Abstract

ABSTRACT 3436/CHENP/2005 "A PROCESS FOR MANUFACTURING AN ELECTRODE" The present invention relates to a process for manufacturing an electrode comprising depositing on an electrode substrate a binder dispersion comprising a precursor of a conductive or semieonductive oxide, forming a conductive or semi conductive oxide coaling from the precursor on the electrode substrate, depositing an elcctroconductive titanium oxide and electrode particles on the conductive or semi conductive oxide coating, adhering the eleclroconduetive titanium oxide and the electrode particles to the formed conductive or semi conductive oxide coating. The invention also relates to an electrode obtainable by the process.

Full Text

The present invention relates to an electrode, a process of manufacturing the electrode, and the use thereof. Background of the invention Electrodes for use in industrial electrolysis, water electrciysis, and other electrolytic processes such as a platinum group metal oxide coated electrode usually have a low electric resistance at high currents. However, such electrodes usually have a short durability. US 4,568,568 discloses a method of plasma spray coating particles on an electrode substrate involving heating the particles at temperatures up to 6000 °C, which then collide with the substrate at a high speed, whereby the particles partially melt and produce a layer of even thickness on the substrate. The particles do not impart an increased surface area to the obtained electrode. The present invention intends to solve the drawbacks of the prior art and to provide a particle coated electrode having increased specific surface area, stability and performance, which finds a great number of applications. The invention also intends to provide a convenient and reliable process of adhering particles to an electrode in a cost-effective way. A further intention of the invention is to provide s process which enables adhering particles to an electrode without deforming the shape of the particles. The invention The present invention relates to a process for manufacturing an electrode comprising depositing on an electrode substrate a binder dispersion comprising a precursor of a conductive or semi conductive oxide, fomenting a conductive or semlconductjve oxide coating from the precursor on the electrode substrate, depositing an electro conductive titanium oxide and electrode particles on the conductive or semi conductive oxide coating, adhering the electro conductive titanium oxide and the electrode particles to the formed conductive or semi conductive oxide coating. By the term "dispersed" as used herein is comprised besides ordinary dispersions, suspensions and slurries of particles, also solutions of e.g. oxide forming precursors. According to one embodiment, the conductive or semi conductive oxide is adhered by decomposing the precursor, preferably by thermally decomposing it. However, the precursor can also be precipitated resulting in the formation of an oxide from the original precursor which may be e.g. a hydroxide or hydrated oxide of titanium or other suitable metal. The material of the electrode substrate may be of any conductive element which can retain Its physical integrity during the manufacturing and its subsequent use in e.g. an electrolytic cell and which preferably can resist alkaline and acidic electrolytes. Suitable electrode substrate materials include electrically conductive metals such as copper, nickel, valve metals such as titanium, tantalum, zirconium or niobium, and alloys or mixtures thereof, preferably titanium or alloys thereof. The configuration of the electrode substrate used is not critical. A suitable electrode substrate may, for example, take the form of a flat sheet or plate, a curved surface, a convoluted surface, a punched plate, a woven wire screen, an expanded mesh sheet, a rod, or a tube. However, the electrode substrate preferably has a planar shape, most preferably in the fond of a sheet, mesh or plate. The electrode substrate can be roughened by means of sand blasting, grit blasting, chemical etching and the like. The use of chemical etchings is well known and such etch ants include most strong Inorganic acids, such as hydrochloric acid, euphoric acid, nitric acid and phosphoric acid, but also organic acids such as oxalic acid. The precursor of the conducting or semi conducting oxide, which can be in the fen of 3 dissolved salt or acid, can be dissolved in an acidic aqueous or organic dispersion or mixtures thereof. Preformed organic dispersions include alcohols such as iso-propanoi, n-propane, or butanes, or mixtures thereof. Organic salts or acids are preferably dissolved in an organic solvent, most preferably in an alcohol as described herein, whereas inorganic salts and acids preferably are dissolved in a substantially aqueous dispersion. Preferably, the organic and/or aqueous binder dispersions have a pH from about 0.5 to about 4, most preferably from about 0,5 to about 2. Preferably, the btnder dispersion has a metal concentration from about 10 to about 200, most preferably from about 20 to about 30 g metal /I, The precursor may be any suitable organic and/or inorganic salt or acid Preferably, the precursor is a mixture of at least two organic and/or inorganic salts or acids of titanium, tantalum, tin, antimony, indium and tin salts, preferably of titanium and tantalum. Preferably, buthyl or ethic titan ate and butyl or ethyl tantalite are employed in combination. According to one embodiment, butyl titan ate and butyl tantalite are employed in combination. The molar ratio of titanium to tantalum suitably is from about 9:1 to about 7:3, preferably from about 9:1 to about 8:2. Precursors of organic salts and/or acids are preferred, since their corresponding conductive or semi conductive oxides can be formed at a lower temperature. This is preferred because a low heating temperature renders the eiectroconductive titanium oxide particles less oxidised resulting in higher electroconductivity. According to one embodiment, electroconductive titanium oxide is suspended in the binder dispersion. As a result, a conductive or semiconductive oxide coating binding an evenly dispersed electro conductive titanium oxide will be finned on the electrode substrate. This may be advantageous to better adhere subsequently deposited electrode particles, because tie electroconductive titanium oxide particles, which preferably are smaller than the electrode particles, surround the electrode particles and thus impart better adhesion between the electrode substrate, the electroconductive titanium oxide particles and the electrode particles, due to an increased contact area. According to one embodiment, the precursor is thermally decomposed at a temperature from about 300 to about 600, more preferably from about 450 to about 500 °C- However, if the precursor is a colloidal solution, e.g. a slightly alkaline alcohol solution of alloy-titanium and tantalum in ammonia, the decomposition can be carried out at a temperature from about 300 to about 450 °C. This lower temperature is possible probably due to the fact that colloidal solutions such as colloidal hydroxide or hydrated oxides solutions can be transformed to oxides by means of dehydration. According to one embodiment, electroconductive titanium oxide and electrode particles suspended in an aqueous or organic dispersion, preferably an aqueous dispersion, are deposited on the formed conductive or semiconductive oxide coating. According to one embodiment, electroconductive titanium oxide and electrode particles are suspended in the binder dispersion resulting in adhesion of electrode particles to the oxide coating formed from the precursor. In order to get a thicker conductive or semiconductive oxide coating, the deposition procedure can be repeated, preferably at least 2 times, most preferably at least 4 times. Preferably, the thickness of the oxide is from about 2 to about 4 \im. According to one embodiment, the electroconductive titanium oxide has a particle size from about 0.1 to about 100, more preferably from about 1 to about 20, even more preferably from about 5 to about 20 Jim, and most preferably from about 5 to about 10 nm. The electroconductive titanium oxide preferably is substantially in magnolia phase (including various oxides such as Ti407 and Tioga) and/or TiO depending on where the electrode to be manufactured will be used. Magnolia phase titanium oxide is preferably used for manufacturing electrodes for use in strongly acidic electrolytes such as sulphuric or nitric acid, due to its capability of resisting con-olive environme-rs, TIO is preferably used in electrodes for use in electrolytes with a pH above about 1,5. Hiectroconductive titanium oxide can be prepared from conventional sintering mixtures of nonconductive titanium oxide (Job) in commercially available futile or anabases phase and titanium metal at a temperature of 1000 to 1500 °C in vacuum. Electroconductive titanium oxide may also be prepared by mixing pulverized Tics in retiled phase and agate mortar followed by sintering. The obtained electroconductive titanium oxide powder contains a mixture of Timor, TI4O7 and/orthicon. The term "electrode particles" as used herein means are electro conductive and have a catalytic activity. The material may be diamond, e.g. boron doped diamond, titanium oxide such as titanium oxide in mangle phase (Bone™), tin dioxide, magnetite {Felon, Ni-ferrite, p-lead dioxide (p-Pb02), BN, WC, Sick, and/or mixtures thereof, preferably diamond. Suitably, the electrode particles have a size from about 0,5 to about 100, preferably from about 1 to about 20, and most preferably from about 5 to about 10 fem. Diamond particles may be obtained from conventional diamond synthetic processes at high temperature and high pressure. According to one preferred embodiment, two different layers are applied on the conductive or semiconductive oxide coating to provide an under layer suitably comprising electroconductive titanium oxide and a top layer of electrode particles to increase the stability of the electrode and more firmly adhere the electrode particles. According to a preferred embodiment, a roughened, blasted and pickled electrode substrate is painted with a binder dispersion comprising a precursor of a semi conducting oxide of a titanium oxide which is subsequently decomposed at a temperature of from about 500 to about 600 °C to form a conductive oxide before depositing a slurry of electroconductive titanium oxide having a titanium content of about 3 to about 20 times of the metal content of the binder dispersion followed by thermal treatment at 400 to 500 °C for 10 min. Subsequently, in a second step, a dispersion comprising about 50 wt% electrode particles and about 50 wt% electroconductive titanium oxide is deposited on the oxide coating and thermally treated to adhere the electroconductive titanium oxide and the electrode particles to the formed titanium oxide coating. According to one embodiment, the second step is repeated at (east 2 times, preferably at least 3 times. The obtained electrode can be further stabilized in vacuum or inert atmosphere, e.g. in argon gas at a temperature from about 500 to about BOO °C. The invention further relates to an electrode obtainable from the process as described herein. The invention further relates to an electrode comprising an electrode substrate, a conductive or semiconductive oxide adhered to the electrode substrate, anc electrode (jaiuucB din tiiet;iiuc;uriauL;iivB Liieiiiiufii Xidex adhered to the conductive or semiconductive oxide coating. The electrode substrate, the conductive or semiconductive oxide, the eiectroconductive titanium oxide, and the electrode particles preferably are as described herein. According to one embodiment of the invention, the conductive or semiconductive oxide may contain several oxide layers, preferably two oxide layers. According to one embodiment, a first layer of oxide coating comprises eiectroconductive titanium oxide and electrode particles. The oxide coating of the first layer may contain from about 10 to about 70, preferably from about 40 to about 60 VLft% electrode particles. The first layer may contain from about 20 to about 80, preferably from about 30 to about 60 wt% eiectroconductive titanium oxide. Preferably, a second layer suitably comprises from about 30 to about 80, preferably from about 50 to about 70 w% electrode particles. Preferably, the remaining part of the second layer is covered with eiectroconductive titanium oxide. According to one embodiment, the content of eiectroconductive titanium oxide is from about 20 to about 70, preferably from about 30 to about 50 wt% based on the weight of the oxide coating. Preferably, the deposition of electrode particles is from about 10 to about 500, more preferably from about 50 to about 100 g/m^ electrode substrate area. Preferably, the deposition of eiectroconductive titanium oxide is from about 5 to about 200, mare preferably from about 10 to about 100 g/m^ electrode substrate area. It has been found that the ordained electrodes can remain stable even in corrosive atmosphere under high potentials of more than 2V vs. NHE and high currents. This may be due to the fact that the oxide formed from the binder dispersion adheres particles of eiectroconductive titanium amide, which in turn, possibly in combination with the oxide coating formed from the binder solution, adhere the electrode particles. According to one embodiment, the electrode has a second layer comprising eiectroconductive electrode particles of diamond, tin dioxide, magnetite (^6304, nickel ferrite, p-lead dioxide, titanium oxide, BN, WC, SiC, SisN^ or mixtures thereof, preferably of titanium oxide and/or diamond, and most preferably diamond. The electrode can take any shape. However, a planar electrode will be prefen-ed for most applications. Preferably, the electrode dees not comprise bi-metal spinel in any of its layers. Preferably, the electrode does not comprise any platinum group metals or oxides thereof since this may lead to passivity problems. The invention also relates to the use of an electrode in an electrolytic cell, for electrolytic processes in water treatment, secondary battery, such as in redox flow cells, and electrolytic ozone generation. Particuiarly, electrodes provided with eiectrode particles of boron doped diamond can be used as anodes for generation of oxygen, ozone, hydrogen peroxide, hydroxyl radicais; in water electrolysis, water treatment, and electroorganic synthesis due to its good electric conductivity as p-type semiconductor. As a cathode, the eiectrode is preferably used for electroorganic synthesis, formation of OH radicals, various oxidation processes, redox flow battery for power storage, and normalization of power consumption. The invention being thus described, it will be obvious that the same may be varied in many ways, Such variations are not to be regarded as a departure from the gist and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the claims. The following examples will further illustrate how the described invention may be performed without limiting the scope of it. Example 1 A titanium plate with a thickness of 1 mm was grit-blasted to a surface roughness of Ra=5 ^m, and pickled with sulphuric acid in order to prepare an eiectrode substrate. A binder solution comprising TiCi4 and TaCls, dissolved in a 10 vrt% HCI solution, was applied on the electrode substrate and heated at 540 "C for 10 min. The coating and heating steps were repeated 4 times resulting in an oxide film of 0.2 jim on the electrode substrate of tantalum and titanium oxides In a molar ratio of Ta to Ti of 1 to 9. A slurry was prepared by suspending an electroconductive titanium oxide powder in a HCI solution of penta-butyl tantalite and tetra-butyi titanate with a molar ratio of Ti to Ta of 8 to 2. The weight ratio of electroconductive titanium oxide to the total Ti and Ta metal content in the binder dispersion was 20:1. The dispersion was stirred and painted on the oxide film. After drying, the electrode was first heated at 60 °C for 10 min, then heated at 450 "C for 10 min, A porous oxide coating of 60 g/m^was obtained having a specific surface area of 10m^/m^ projected substrate area. On the poriDus oxide coating a siurry prepared from 50 wt% electroconductive titanium oxide and 50 wt% boron doped electroconductive diamond powder with an average particle size of 7 to 10 nm was applied- The slurry was subsequently dried and heated at 450 °C far 10 min. The deposition of the slurry was repeated once followed by the same heat treatment. The obtained electrode snowed to work well in a continuous electrolysis process at a cun-ent density of 1A/dm^ Example 2 An electrode was prepared by depositing electroconductive titanium oxide on the titanium electrode substrate prepared in the same way as in example 1, An eiectroconductive titanium oxide powder was suspended in a binder dispersion containing titanium tnchlonde and penta-butyl tantalite having a molar ratio of titanium to tantalum of 9 to 1. The weight ratio of eiectroconductive titanium oxide to the total Ti and Ta metal content in the binder dispersion was 20 to 1. The binder dispersion was applied on the electrode sutJstrate which was subsequently dried In air at room temperature followed by drying at 60 °C and heat treatment at 500 °C. The application of the binder solution was repeated three times. An eiectroconductive titanium oxide layer (substantially as Ti407) was fomied under the same conditions as in example 1, in which the coating amount was 60 g/m^ substrate area. Then, an eiectroconductive titanium oxide layer was formed from magneli phase titanium oxide particles having a size of 5 to 10 nm, which were suspended in a slurry, and then coated and heat treated at 450 "C for 10 minutes as in example 1. This procedure was repeated three times resulting in a total deposition of 50 g titanium metal Irn^ substrate area. The electric conductivity of the electrode was somewhat higher than the electrode of example 1 due to the electrode materials. The active surface area was increased to 20 m^/m^ electrode substrate area. Then, continuous electrolysis was performed at a current density of 2 A/dm^. Example 3 An electrode according to example 2 was prepared, except far the electrode particles which were of tin oxide and antimony oxide in rufile phase in a molar ratio of tin to antimony of 9:1. The electrode was tested in sulphuric add electrolyte containing 100 ppm phenol and showed to work since decomposition of phenol could be observed. Example 4 An electrode was prepared in accordance with example 1 except for the diamond particles which were replaced by TiO particles. Continuous electrolysis was perfomned in a HzS04 solution at a current density of 3A/dm^. Example 5 An electrode substrate was prepared as shown in example 1. The binder dispersion was prepared by mixing acidic solution of tetra buthoxi-titanate and penta buthoxi tantalite in a molar ratio of 8 to 2 which then was neutralized with ammonia. The solution turned hazy white and colloidal precipitation was detected. Then, butyl alcohol was added to the hazy liquid containing hydrated titanium-tantalum co-cxice to adjust the total metal content of the liquid to 15 g/l. The obtained liquid had a viscosity of 10 to 20 c-poise. Then, electroconductive titanium oxide was mixed into the dispersion whioh subsequently was applied with a brush to the electrode substrate. After drying, the substrate was heat treated at 300 "C in air atmosphere resulting in a deposition of 50 g electroconductive titanium oxide/ m2 substrate area. Then 70 wt% of electroconductive titanium oxide and 30 wt% p-Pb02 particles, whose average particle size was 10 to 12 ^m, was applied onto the oxide coated substrate. The substrate was then dried and heat treated. Then, 20 g |3-lead dioxide/m^ was deposited. The obtained electrode had a surface area of 8 m^/m^ electrode substrate, and couid be used as anode in continuous electrolysis at a current density of lOA/dm^. Example 6 A tin dioxide particle electrode was prepared by the same process 3s in example 5, but where p-lead dioxide was replaced by tin dioxide. The tin dioxide was obtained by co-precipitation of 90 mol% of tin letra-chloride (SnCU) and antimony-penta-chloride in ethyl alcohol by neutralization with ammonia. About 1 mol% of iridium chloride was then added to the dispersion. Then, the dispersion was dried followed by heat treatment at 400 "C for 30 minutes in air, A black coloured electroconductive tin dioxide was obtained. Then, this tin dioxide was crushed and ground with agate mortar. The obtained tin dioxide powder was co-deposited with electroconductive titanium oxide on the electrode substrate. The surface area of this electrode was 7 to 9 m2/m2 eiectrode substrate. The electrode was then used at a current density of 2 A/m2 and showed to wor( WE CLAIM; i. A process for manufacturing an electrode comprising the steps of a) depositing on an electrode substrate a binder dispersion comprising a precursor of a conductive or semi conductive oxide b) forming a conductive or semi conductive oxide coating from said precursor on the electrode substrate c) depositing an electro conductive titanium oxide and electrode particles on the conductive or semi conductive oxide coating d) Adhering the electro conductive titanium oxide and the electrode particles to the formed conductive or semi conductive oxide. 2. The process as claimed in claim 1, wherein the binder dispersion comprises a precursor of titanium or tantalum oxides. 3. The process as claimed in claim 1 or 2, wherein the binder dispersion comprises a precursor of titanium and tantalum oxides. 4. The process as claimed in any of claims 1-3, wherein said precursor is thermally decomposed at a temperature from about 300 to about 600 °C. 5. The process as claimed in any of claims 1-4, wherein the electro conductive titanium oxide substantially is Tao. 6. The process as claimed in any of claims 1-5, wherein the electrode particles comprise electro conductive titanium oxide. 7. The process as claimed in any of claims 1-6, wherein the electrode particles comprise electro conductive diamond. 8. Electrode obtainable by the process as claimed in any of claims I to 7.

Documents:

3436-chenp-2005 abstract duplicate.pdf

3436-chenp-2005 abstract.pdf

3436-chenp-2005 claims duplicate.pdf

3436-chenp-2005 claims.pdf

3436-chenp-2005 correspondence-others.pdf

3436-chenp-2005 correspondence-po.pdf

3436-chenp-2005 description (complete) duplicate.pdf

3436-chenp-2005 description (complete).pdf

3436-chenp-2005 form-1.pdf

3436-chenp-2005 form-18.pdf

3436-chenp-2005 form-26.pdf

3436-chenp-2005 form-3.pdf

3436-chenp-2005 form-5.pdf

3436-chenp-2005 pct.pdf

3436-chenp-2005 petition.pdf