WO2000028114A1 - Electrodeposition of catalytic metals using pulsed electric fields - Google Patents
Electrodeposition of catalytic metals using pulsed electric fields Download PDFInfo
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- WO2000028114A1 WO2000028114A1 PCT/US1999/025611 US9925611W WO0028114A1 WO 2000028114 A1 WO2000028114 A1 WO 2000028114A1 US 9925611 W US9925611 W US 9925611W WO 0028114 A1 WO0028114 A1 WO 0028114A1
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- Prior art keywords
- pulses
- cathodic
- hertz
- anodic
- duty cycle
- Prior art date
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 60
- 239000002184 metal Substances 0.000 title claims abstract description 60
- 230000003197 catalytic effect Effects 0.000 title claims abstract description 50
- 238000004070 electrodeposition Methods 0.000 title abstract description 16
- 150000002739 metals Chemical class 0.000 title description 7
- 230000005684 electric field Effects 0.000 title description 6
- 238000009792 diffusion process Methods 0.000 claims abstract description 35
- 239000000758 substrate Substances 0.000 claims abstract description 28
- 239000000446 fuel Substances 0.000 claims abstract description 20
- 239000012528 membrane Substances 0.000 claims abstract description 12
- 150000002500 ions Chemical class 0.000 claims abstract description 10
- 239000003054 catalyst Substances 0.000 claims description 99
- 238000000034 method Methods 0.000 claims description 85
- 239000002245 particle Substances 0.000 claims description 63
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 33
- 238000000151 deposition Methods 0.000 claims description 20
- 238000011068 loading method Methods 0.000 claims description 18
- 239000003792 electrolyte Substances 0.000 claims description 16
- 229910052697 platinum Inorganic materials 0.000 claims description 16
- 229920005989 resin Polymers 0.000 claims description 15
- 239000011347 resin Substances 0.000 claims description 15
- 229910045601 alloy Inorganic materials 0.000 claims description 8
- 239000000956 alloy Substances 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 8
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 5
- 229910052703 rhodium Inorganic materials 0.000 claims description 4
- 239000010948 rhodium Substances 0.000 claims description 4
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 4
- 239000010419 fine particle Substances 0.000 claims description 3
- OYJSZRRJQJAOFK-UHFFFAOYSA-N palladium ruthenium Chemical compound [Ru].[Pd] OYJSZRRJQJAOFK-UHFFFAOYSA-N 0.000 claims 3
- 239000002105 nanoparticle Substances 0.000 claims 1
- 238000007747 plating Methods 0.000 abstract description 19
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 12
- 229910052799 carbon Inorganic materials 0.000 description 12
- 230000008021 deposition Effects 0.000 description 12
- 229910021645 metal ion Inorganic materials 0.000 description 8
- 239000003153 chemical reaction reagent Substances 0.000 description 6
- 230000006911 nucleation Effects 0.000 description 5
- 238000010899 nucleation Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000010970 precious metal Substances 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000009713 electroplating Methods 0.000 description 3
- 229920002313 fluoropolymer Polymers 0.000 description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000002209 hydrophobic effect Effects 0.000 description 2
- 229920000554 ionomer Polymers 0.000 description 2
- 239000002923 metal particle Substances 0.000 description 2
- 239000000376 reactant Substances 0.000 description 2
- 230000036647 reaction Effects 0.000 description 2
- 239000007784 solid electrolyte Substances 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 238000009388 chemical precipitation Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 1
- 239000004811 fluoropolymer Substances 0.000 description 1
- UQSQSQZYBQSBJZ-UHFFFAOYSA-N fluorosulfonic acid Chemical compound OS(F)(=O)=O UQSQSQZYBQSBJZ-UHFFFAOYSA-N 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000003863 metallic catalyst Substances 0.000 description 1
- 239000002159 nanocrystal Substances 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000002952 polymeric resin Substances 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8803—Supports for the deposition of the catalytic active composition
- H01M4/8807—Gas diffusion layers
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/18—Electroplating using modulated, pulsed or reversing current
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/615—Microstructure of the layers, e.g. mixed structure
- C25D5/617—Crystalline layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/8605—Porous electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8825—Methods for deposition of the catalytic active composition
- H01M4/8853—Electrodeposition
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0082—Organic polymers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Definitions
- This invention relates to electrodeposition of metals in a finely divided state and more particularly to electrodeposition of catalytic metals for fuel cell electrodes.
- GDEs gas diffusion electrodes
- PEMFCs proton exchange membrane fuel cells
- a major factor in the cost of PEMFCs is the expense of the electrodes.
- the cost of the electrodes is determined by a number of factors, principally the expense of the precious metal catalysts, which are needed for practical efficiency, and the cost of fabricating the electrodes, which is typically conducted by means of a batch process.
- the cost of the fuel cell system is also greatly affected by the electrochemical performance of the electrodes which determines the power density of the fuel cell, i.e., the power produced per unit area, e.g., kilowatts per square centimeter.
- the combination of power density, catalyst loading and system fabrication costs determines the ultimate cost per kilowatt of the complete fuel cell system.
- Patent 5,084,144 to Vilambi-Reddy et al., the entire disclosure of which is incorporated herein by reference.
- fine particles of a catalytic metal are deposited electrolytically onto an uncatalyzed layer of carbon particles, bonded with a fluorocarbon resin and impregnated with the proton exchange resin, by contacting the face of the electrode with a plating bath and using pulsed direct current.
- the gas diffusion electrodes prepared by the process of U.S. Patent 5,084,144 contained about 0.05 mg/cm 2 of platinum as particles of about 3.5 nanometers in diameter having a surface area of about 80 m 2 /g.
- Such electrodes functioned about as well as the electrodes using supported platinum with a loading of 0.5 mg/cm 2 of platinum. It is believed that these electrodes achieved their improved mass activity, i.e., current per weight of platinum, because the electrolytic process deposits the catalyst particles only at regions with both electronic and ionic accessibility. Such locations are expected to be accessible to the protons and electrons required for the fuel cell reactions. However, such improved mass activity does not compensate for the low catalyst loading provided by the process of U.S. Patent 5,084,144. Consequently, the power density of such electrodes is still insufficient to permit the wide use of PEMFCs as sources of electric power.
- a further object is to provide a method for preparing gas diffusion electrodes having high catalytic activity.
- a further object is to provide a gas diffusion electrode having high catalytic activity.
- a further object is to provide a gas diffusion electrode having a metallic catalyst in finely divided form.
- a further object is to provide a method for electrodepositing a catalyst on a substrate in finely divided form.
- a further object is to provide a method of preparing a gas diffusion electrode that can provide adequate power density in a proton exchange membrane fuel cell with economical catalyst loading.
- a further object is to provide a method of preparing a gas diffusion electrode by a continuous electroplating process.
- Figure 1A illustrates a pulse current waveform used in the method of the invention.
- Figure IB illustrates a waveform of modulated reverse electric current used in a preferred embodiment of the method of the invention.
- Figure 2A illustrates a cross-section of the catalyst support structure of the gas diffusion electrode of the invention before the catalytic metal is deposited.
- Figure 2B illustrates a cross-section of the gas diffusion electrode of the invention after the electrodeposition of the catalytic metal.
- Figure 3 illustrates schematically a cross section of an electroplating cell arranged for electrodeposition of a catalytic metal onto the catalyst support member.
- Figure 4 illustrates schematically the reel-to-reel electrodeposition method of the invention.
- a gas diffusion electrode having low catalyst loading and good availability of catalyst to reagents is prepared by an electrodeposition process.
- a GDE according to the invention may be prepared by first applying to an electrically conductive, gas-permeable backing layer a layer of conductive particles, e.g., carbon particles, as a catalyst support, using as a binder for the carbon particles a proton exchange polymer. Then, small particles of a catalytic metal or alloy are deposited electrolytically by contacting the catalytic face of the electrode with an electrolyte containing the metal to be deposited.
- the electrolyte bath contains a counterelectrode, which may be an inert electrode. An electric current is passed between the counterelectrode and the membrane electrode in order to deposit the catalytic metal on the surface of the carbon particles within the binding ionomer.
- the first step is the electrolytic reduction of metal ions in the solution immediately adjacent to the substrate to metal atoms and the deposition of these atoms on the surface as adatoms.
- the adatoms then aggregate into small nuclei that form the centers for further deposition of metal from the plating bath. Because the overpotential required for nucleation is significantly greater than that for deposition of metal on previously formed nuclei, crystal growth on the nuclei is favored over the formation of additional nuclei. Consequently, in conventional electrolytic deposition, the catalytic metal tends to be deposited in relatively large crystals having a relatively small specific surface area.
- deposition of the catalytic metal or alloy as small particles is favored by conducting the electrolytic deposition on a cathodic substrate using a pulsed electric field with short on-time and/or short duty cycle.
- a reversing electric field pulse (anodic) may be interposed between at least some of the forward pulses.
- FIG. 1A A schematic representation of a rectangular modulated electric field waveform used in the process of the invention is illustrated in Figure 1A.
- the waveform comprises a train of cathodic pulses having a short on-time and/or a short duty cycle.
- FIG. IB A schematic representation of a rectangular modulated reverse electric field waveform used in a preferred process of the invention is illustrated in Figure IB.
- the waveform of Figure IB essentially comprises a cathodic (forward) pulse followed by an anodic (reverse) pulse.
- An off-period or relaxation period may follow either or both of the cathodic and anodic pulses.
- the ordinate in Figures 1A and IB could represent either current or voltage. Although it is generally more convenient in practice to control the voltage, the technical disclosure of the process is more straightforward if discussed in terms of the current flow.
- the waveform need not be rectangular as illustrated.
- the cathodic and anodic pulses may have any voltage-time (or current-time) profile.
- rectangular pulses are assumed for simplicity.
- the point in time chosen as the initial point of the pulse train is entirely arbitrary.
- Either the cathodic pulse or the anodic pulse (or any point in the pulse train) could be considered as the initial point.
- the representation with the cathodic initial pulse is introduced for simplicity in discussion.
- the cathodic peak current is shown as ii and the cathodic on-time is ti.
- the anodic peak current is shown as i 2 and the anodic on-time is t 2 .
- the relaxation time, or off-times are indicated by t a , and tb.
- the inverse of the period of the pulse train (1/T) is the frequency (/) of the pulse train.
- the ratio of the cathodic on-time to the period (ti/T) is the cathodic duty cycle (Di)
- the ratio of the anodic on-time to the period (t 2 /T) is the anodic duty cycle (D 2 )
- the current density, i.e., current per unit area of the electrode, during the cathodic on-time and anodic on-time is known as the cathodic peak pulse current density and anodic peak pulse current density, respectively.
- the cathodic charge transfer density (Qi) is the product of the cathodic current density and the cathodic on-time (iiti)
- the anodic charge transfer density (Q 2 ) is the product of the anodic current density and the anodic on-time (i 2 t 2 )
- the average current density (i a v e ) is the average cathodic current density (iiti) minus the average anodic current density (i 2 t 2 ) . Accordingly the relationships among the parameters may be represented by the following equations.
- i ave i i Di - i 2 D 2 ( 5 ;
- the cathodic duty cycle should be relatively short, less than about 40 %, and the cathodic pulses should be relatively short to favor nucleation over deposition of additional metal on preexisting nuclei.
- the cathodic on-time should range from about
- the cathodic duty cycle is from about 1 % to about 30 %, more preferably from about 2 % to about 20 % and still more preferably from about 5 % to about 15 %.
- the anodic on-time and duty cycle may vary widely.
- the anodic duty cycle is less than 90 %, preferably from about 1 % to about 90 %, more preferably about 15 % to about 50 %, more preferably from about 20 % to about 40 % .
- the anodic on-time may also vary widely and will in general be determined by the anodic duty cycle and the frequency.
- the cathodic-to-anodic net charge ratio will be greater than one, in order to provide a net deposition of metal on the surface .
- the frequency of the pulse train used in the method of the invention may range from about 10 hertz to about 5000 hertz, preferably from about 50 Hz to about 5000 Hz, more preferably from about 100 Hz to about 3000 Hz, and still more preferably from about 500 hertz to about 1500 hertz.
- an anodic pulse is introduced between at least some of the cathodic pulses.
- two or more cathodic pulses may occur between a pair of anodic pulses.
- the period of a pulse train comprised of such pulse groups may conveniently be defined as the time from the beginning of one cathodic pulse to the beginning of the next cathodic pulse that is similarly situated in the pulse train.
- the frequency of the pulse train may then be defined as the reciprocal of the period, as discussed above.
- the frequency of the pulse train may range from about 0.5 Hz to about 5000 Hz, or in preferred embodiments the frequency may range from about 10 hertz to about 5000 hertz, preferably from about 50 Hz to about 5000 Hz, more preferably from about 100 Hz to about 3000 Hz, and still more preferably from about 500 hertz to about 1500 hertz.
- the pulse width, duty cycle, and applied voltage of the cathodic and anodic pulses must be adjusted to provide that the overall process is cathodic, i.e., there is a net deposition of metal on the substrate catalyst support.
- the practitioner will adapt the pulse width, duty cycle, and frequency to a particular application, based on the principles and teachings of the process of the invention.
- FIG. 2A illustrates an uncatalyzed gas diffusion electrode (GDE), i.e., a gas diffusion electrode before the catalytic metal is deposited thereon.
- the uncatalyzed GDE 200 comprises an electrically conductive backing layer 202 to which is adhered a catalytic layer 204 comprising particles 206 of an electrically conductive catalyst support, e.g., carbon particles, which are in electrical contact with one another and with the backing layer 202.
- the backing layer 202 may be any porous electrically conducting material that will permit reactant gas to diffuse therethrough to contact the supported catalyst.
- the backing layer 202 is typically a carbon paper or carbon cloth that has been rendered hydrophobic by coating with a fluorocarbon polymer by conventional procedures.
- the catalyst support particles 206 may be any electrically conductive particles that can accept nanocrystals of a catalytic metal such as platinum.
- the catalyst support particles 206 are distributed in a binder 208 comprising a proton exchange resin.
- a binder 208 comprising a proton exchange resin.
- resins are well known and may be, for example, a perfluorosulfonate ionomer such as that sold by E.I. du Pont de Nemours & Co. under
- the catalyst support layer 204 may be prepared by the conventional procedure of dispersing the catalyst support particles 206 in a solution of the proton exchange resin 208, coating the solution onto the backing layer 202, and drying the coated layer. The dried layer maybe subjected to a heat treatment to improve its physical characteristics.
- Figure 2A shows a preferred embodiment of the invention wherein the uncatalyzed catalyst support particles are dispersed in a proton exchange resin that serves as both binder and electrolyte
- a proton exchange resin that serves as both binder and electrolyte
- the process of the invention is also applicable to gas diffusion electrodes wherein the catalyst support particles are bonded to the backing layer by an inert binder, e.g., a fluorocarbon polymer resin, and the proton exchange resin is subsequently applied by a conventional procedure such as coating, spraying, painting, impregnation or the like.
- the uncatalyzed gas diffusion electrode may be prepared by the process of U.S. Patent 5,211,984, to Wilson, or U.S.
- Patent 5,234,777, to Wilson both of which are incorporated herein by reference.
- the uncatalyzed gas diffusion electrode 200 is impregnated with a catalytic metal by the process of the invention as illustrated in Figure 3.
- An electroplating cell 212 is prepared having a counterelectrode 216 and containing a plating bath 214 comprised of a solution of suitable ions of the catalytic metal to be deposited on the support particles 206.
- the catalyst support layer 204 of the uncatalyzed GDE 200 is contacted with the surface of the plating bath 214. Care is taken to avoid immersing the backing layer in the bath 214 in order to avoid depositing catalytic metal in inactive locations.
- the general procedure for electrolytically depositing a metal catalyst onto a gas diffusion electrode is disclosed in U.S. Patent 5,084,144, referred to above.
- the backing layer 202 and the counter electrode 216 are connected to the terminals 220 of a power supply 218 by connecting wires 222.
- the power supply 218 provides a pulsed forward or cathodic voltage having a short on-time and/or short duty cycle to the GDE 200, or a reversing pulsed voltage wherein the forward pulses have a short duration and typically a short duty cycle.
- adatoms are deposited on the catalyst support particles 206 and form nuclei for further deposition of the catalytic metal.
- the ions of the catalytic metal can diffuse from the bulk phase toward the GDE and restore the bulk concentration of ions at the surface of the catalyst support particles 206.
- the metal ions are deposited both on the preexisting nuclei and on the surface of the catalyst support particles to form additional nuclei.
- the voltage (or current) applied should be relatively large. It is known that the rate of formation of nuclei on a substrate in electrodeposition is governed by the equation
- N number of nuclei
- i current density corresponding to the nucleation rate
- k nucleation constant
- t time.
- the rate of formation of nuclei is 1) directly proportional to the current density (or inversely proportional to the duty cycle) and 2) inversely proportional to the time (or directly proportional to the frequency) . Consequently short on-times and short duty cycles will favor nucleation.
- an anodic pulse may be introduced between at least some of the cathodic pulses.
- the off-time allows the replenishment of the metal concentration at the surface of the substrate as pointed out above.
- some of the metal atoms in the nuclei will be reoxidized and dissolved into the electrolyte. Because the local concentration of the metal ions at the surface of the catalyst support particles 216 is restored to that in the bulk phase during the off time preceding the anodic pulse, the concentration of metal ions adjacent to the surface of the catalytic particles 206 will now exceed the bulk phase concentration.
- any metal ions removed from relatively large nuclei formed during the initial pulse may diffuse to adjacent areas of the surface, increasing the metal ion concentration in those areas.
- metal ions close to the surface of the catalytic particles 206 will again be precipitated onto the surface of the particles to form additional nuclei in those locations. Some of the ions will plate onto the existing nuclei, but additional nuclei will also be formed at other points on the surface of the particles 206.
- t b in Figure 1 there may be an off-time (t b in Figure 1) between the anodic pulse and the succeeding cathodic pulse to allow for additional lateral diffusion of the metal ions, it is preferred that the anodic pulse be immediately succeeded by a cathodic pulse, (i.e., t b is preferably zero), so that any redissolved ions do not have time to diffuse back into the bulk phase of the plating bath 214.
- the catalyzed gas diffusion electrode i.e., having catalytic metal deposited on the catalyst support particles 206, is shown schematically in Figure 2B.
- Catalyst particles 210 are distributed throughout the catalyst support layer 204, supported on the catalyst support particles 206. According to the invention catalyst particles are deposited in those locations which are accessible to the electrolyte in the plating bath 214 and which have electrical contact with the backing layer through the electrically conductive support particles 206.
- the catalyst binder is a proton exchange resin 208
- the support layer 204 may be made relatively thin, e.g., not thicker than about 15 micrometers, the gaseous regents can readily diffuse through the proton exchange resin to the catalytic sites.
- the support layer 204 has a thickness ranging from about 0.1 micrometer to about
- micrometers preferably from about 0.3 micrometers to about 10 micrometers, and more preferably from about 0.3 micrometers to about 6 micrometers.
- a catalyst support layer 204 can be prepared using a hydrophobic binder, e.g. a fluoropolymer resin, for the catalyst support particles and coating a layer of a proton exchange resin onto the surface of the layer so prepared.
- a hydrophobic binder e.g. a fluoropolymer resin
- Such catalyst support layers are disclosed in U.S. Patent 5,084,144. Similar catalyst support layers are disclosed in U.S. Patent 4,876,115, to Raistrick (using precatalyzed support particles), the entire disclosure of which is incorporated herein by reference .
- the electrodeposition process is preferably continued until the catalyst loading, i.e., the amount of catalyst per square centimeter of the face of the electrode, ranges from about 0.08 mg/cm 2 of the face of the electrode to about 1.0 mg/cm 2 .
- the catalyst amounts to about 0.1 mg/cm 2 to about 0.4 mg/cm 2 , and more preferably from about 0.1 mg/cm 2 to about 0.3 mg/cm 2 , and still more preferably from about 0.1 mg/cm 2 to about 0.2 mg/cm 2 .
- the pulse width, duty cycle and frequency of the pulse reverse voltage electrodeposition process should be adjusted to provide a particle size of the catalyst particles in the range of from about 3.0 nanometers to about 8.0 nanometers, preferably from about 3.0 nanometers to about 5.0 nanometers.
- the efficiency of the catalyst at the defined catalyst loading provides a rate of reaction that gives a power density, i.e., power produced per square centimeter of electrode, that is optimum for construction of proton exchange membrane fuel cells. It is important to retain the relatively small catalyst particle size and accessibility of the catalyst particles to the gas reagents and the proton exchange membrane that functions as the electrolyte, while providing a catalyst loading in the above-defined range.
- catalyst particles that are chemically deposited on a particulate catalyst support may be of a size similar to that produced by the process of the invention, when they are incorporated into the catalytic layer of the GDE they are less available to the reagents. This may occur because some of the catalyst particles are not in good contact with the proton exchange membrane or because some of the carbon support particles might not be in electrical contact with one another and the backing layer. Evidently such catalyst particles are ineffective and cause the catalyst to be less efficient. This causes increased catalyst expense.
- the electrolytic deposition of catalyst assures that any catalyst particle is in electrical contact with a carbon support particle, and thereby with the backing layer, as well as with the proton exchange membrane, for it is only such locations that are accessible to the electrolyte from which the particles are deposited and the electrons supplied through the backing layer and catalyst support particles.
- merely increasing the amount of catalyst deposited electrolytically by the method of the prior art merely increases the size of the catalyst particles, with the result that the catalyst particles have less active surface area per unit weight than the smaller particles. Consequently, it is necessary to provide a catalyst support layer having both a catalyst loading and a catalyst particle size in the ranges defined above.
- the process of the invention may be used to deposit any conventional catalytic metal or alloy.
- Suitable metals include platinum, palladium, rhodium, ruthenium, and alloys thereof.
- the plating bath may be any conventional plating bath used for electrodepositoin of these metals and alloys.
- Figure 4 shows a preferred embodiment of the process of the invention carried out in a continuous plating apparatus 300.
- the apparatus 300 comprises a plating tank 302 having a counterelectrode 304 and containing a plating bath 306.
- the uncatalyzed gas diffusion electrode 200 is prepared in the form of a continuous web. The web is passed continuously over the surface of the plating bath 306. In the arrangement illustrated in Figure 4, the web of uncatalyzed gas diffusion electrode is supplied on a supply reel 308.
- the web passes over guide and contact reel 312 positioned to place the catalyst support layer containing the uncatalyzed catalyst support particles in contact with the surface of plating bath 306.
- the backing layer 202 of the GDE is in electrical contact with the electrically conductive guide reel 312.
- Power supply 318 provides voltage for the electrodeposition through terminals 320, connections
- the web is moved across the surface of the plating bath at a rate such that it is in contact with the plating bath for a sufficient time for deposition of the predetermined amount of catalytic metal particles.
- the catalyzed gas diffusion electrode 200 then passes over guide reel 314 and is taken up on take-up reel 310.
- the gas diffusion electrode web 200 is moved over the surface of the plating bath 306 by drive means not shown acting on one or more of the supply reel 308, take-up reel 310, and/or guide reels 312 and 314.
- the continuous catalyzed gas diffusion electrode web so prepared may then be used in subsequent operations for the manufacture of fuel cells.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002349242A CA2349242C (en) | 1998-11-02 | 1999-11-02 | Electrodeposition of catalytic metals using pulsed electric fields |
AU29581/00A AU2958100A (en) | 1998-11-02 | 1999-11-02 | Electrodeposition of catalytic metals using pulsed electric fields |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/184,247 | 1998-11-02 | ||
US09/184,247 US6080504A (en) | 1998-11-02 | 1998-11-02 | Electrodeposition of catalytic metals using pulsed electric fields |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2000028114A1 true WO2000028114A1 (en) | 2000-05-18 |
WO2000028114A9 WO2000028114A9 (en) | 2000-09-28 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US1999/025611 WO2000028114A1 (en) | 1998-11-02 | 1999-11-02 | Electrodeposition of catalytic metals using pulsed electric fields |
Country Status (4)
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US (1) | US6080504A (en) |
AU (1) | AU2958100A (en) |
CA (1) | CA2349242C (en) |
WO (1) | WO2000028114A1 (en) |
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US5516415A (en) * | 1993-11-16 | 1996-05-14 | Ontario Hydro | Process and apparatus for in situ electroforming a structural layer of metal bonded to an internal wall of a metal tube |
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1998
- 1998-11-02 US US09/184,247 patent/US6080504A/en not_active Expired - Lifetime
-
1999
- 1999-11-02 AU AU29581/00A patent/AU2958100A/en not_active Abandoned
- 1999-11-02 CA CA002349242A patent/CA2349242C/en not_active Expired - Fee Related
- 1999-11-02 WO PCT/US1999/025611 patent/WO2000028114A1/en active Application Filing
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US5085743A (en) * | 1990-05-02 | 1992-02-04 | Physical Sciences, Inc. | Electrode for current-limited cell, cell including the electrode method for using the cell and a method of making the electrode |
US5084144A (en) * | 1990-07-31 | 1992-01-28 | Physical Sciences Inc. | High utilization supported catalytic metal-containing gas-diffusion electrode, process for making it, and cells utilizing it |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE10228323A1 (en) * | 2002-06-25 | 2004-01-29 | Integran Technologies Inc., Toronto | Patching process for degraded portion of metallic workpiece e.g. pipe and conduit, involves electroplating reinforcing metallic patch to cover degraded portion |
DE10228323B4 (en) * | 2002-06-25 | 2005-06-09 | Integran Technologies Inc., Toronto | Cathodic electrodeposition process and microcomponents made by such a process |
DE10262102B4 (en) * | 2002-06-25 | 2006-06-22 | Integran Technologies Inc., Toronto | Patching process for degraded portion of metallic workpiece e.g. pipe and conduit, involves electroplating reinforcing metallic patch to cover degraded portion |
SG144005A1 (en) * | 2007-01-03 | 2008-07-29 | Agni Inc Pte Ltd | Electro-deposition of catalyst on electrodes |
CN101845657A (en) * | 2009-02-07 | 2010-09-29 | Skf公司 | Coating device |
Also Published As
Publication number | Publication date |
---|---|
AU2958100A (en) | 2000-05-29 |
WO2000028114A9 (en) | 2000-09-28 |
US6080504A (en) | 2000-06-27 |
CA2349242A1 (en) | 2000-05-18 |
CA2349242C (en) | 2010-01-12 |
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