GB2187880A - Electrode for oxidising methanol - Google Patents

Electrode for oxidising methanol Download PDF

Info

Publication number
GB2187880A
GB2187880A GB08704526A GB8704526A GB2187880A GB 2187880 A GB2187880 A GB 2187880A GB 08704526 A GB08704526 A GB 08704526A GB 8704526 A GB8704526 A GB 8704526A GB 2187880 A GB2187880 A GB 2187880A
Authority
GB
United Kingdom
Prior art keywords
electrode
carbon
electrode according
substrate
catalyst
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08704526A
Other versions
GB8704526D0 (en
Inventor
John Bannister Goodenough
Andrew Hamnett
Ramasamy Manoharan
Brendan James Kennedy
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
National Research Development Corp UK
Original Assignee
National Research Development Corp UK
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB868604982A external-priority patent/GB8604982D0/en
Priority claimed from GB868622455A external-priority patent/GB8622455D0/en
Application filed by National Research Development Corp UK filed Critical National Research Development Corp UK
Publication of GB8704526D0 publication Critical patent/GB8704526D0/en
Publication of GB2187880A publication Critical patent/GB2187880A/en
Withdrawn legal-status Critical Current

Links

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
    • H01M4/90—Selection of catalytic material
    • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
    • 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
    • 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
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
    • 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
    • H01M4/96—Carbon-based 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
    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
    • H01M2004/8684—Negative electrodes
    • 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
    • H01M2300/0002—Aqueous electrolytes
    • H01M2300/0005—Acid electrolytes
    • 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
    • H01M2300/0002—Aqueous electrolytes
    • H01M2300/0005—Acid electrolytes
    • H01M2300/0011—Sulfuric acid-based
    • 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
    • H01M2300/0002—Aqueous electrolytes
    • H01M2300/0014—Alkaline electrolytes
    • 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
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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

Abstract

An electrode for oxidising methanol comprises a preferably porous substrate which is an electronic conductor capable of reducing elemental oxygen to water yielding not more than 5% hydrogen peroxide, to which substrate is attached a catalyst comprising platinum and ruthenium, or platinum and titanium dioxide, or all three.

Description

SPECIFICATION Electrode for oxidising methanol This invention relates to an electrode for oxidising methanol, to a fuel cell including such an electrode, to a method of oxidising methanol at such an electrode, and to a method of making certain such electrodes.
According to the present invention, an electrode for oxidising methanol comprises a preferably porous substrate which is an electronic conductor capable of reducing elemental oxygen to water yielding not more than 5% (preferably not more than 1%, more preferably not more than 0.1%) hydrogen peroxide, to which substrate is attached a catalyst comprising platinum and either or both of ruthenium and titanium dioxide.
A preferred suitable substrate is carbon of an ash content less than 0.1%, preferably less than 0.05%, preferably not more than 0.01%. An example of such a carbon is 'coconut carbon', which is derived from coconut shells by converting these to charcoal, washing and comminuting the charcoal, and exposing the comminuted charcoal to gas, preferably first carbon dioxide and optionally afterwards ammonia or the latter by itself. An alternative suitable gas is steam. Another example is carbon (for example sold by Cabot Corporation under the Trade Mark Vulcan XC-72) which is of poorly crystalline type and has a surface area of at least 200 m2/g, a mean particle size in the range 5 mm to 50 mm, and an apparent density of 80 to 110 kg/m3, which may be treated by comminuting it an exposing it to gas at elevated temperature.
Preferably the carbon before the comminution has a surface area of not more than 300 m2/g. Preferably the carbon before the comminution has a pH below 7. The carbon may be exposed to only carbon dioxide, for example at 8000C to 1 000 C, preferably for 40 to 90 minutes, such as 9000for 1 hour.
Catalyst loadings may be 1 to 15% by weight of the substrate, preferably 2 to 12%.
The invention extends to a fuel cell including an electrode as set forth above. The invention also provides a method of oxidising methanol, comprising contacting methanol and water at an electrode as set forth above and applying to the electrode a potential more positive than -0.3 volts with respect to the Hg/Hg2SO4 electrode.
According to another aspect, the invention provides a method of making an electrode as set forth above, comprising applying a solution containing a platinum, and a ruthenium compound onto the substrate and decomposing the compounds, whereby the desired catalyst is precipitated on, and is attached to, the substrate.
Preferably the substrate is mixed with a titanium compound which is decomposed to form titanium dioxide. The invention extends to the electrode so made, and to fuel cells, methods of oxidising methanol etc. using it. For use in alkaline media, the 'coconut' carbon is preferred. For use in acid media, the poorly crystalline carbon is preferred.
The invention will now be described by way of example. In the accompanying drawings, Figures 1 and 2 show the potential versus current density obtained for various electrodes in 2.5M H2SO4, 1 M MeOH. Figure 3 shows the specific activities for some of these electrodes. Figure 4 shows lifetime data. In Figures 1 to 3, some electrodes not according to the invention are included for comparison.
A porous carbon electrode is made utilizing Vulcan XC-72 carbon.
High-surface-area Vulcan XC-72 carbon was obtained from the Cabot Corp., Billerica, MA. The ash content of this carbon was found to be about 0.05%. The other physical and chemical parameters of this carbon are as follows: Surface area 257 m2/g Mean particle size 30 mm Approximate density 96 kg/m3 pH 5 This carbon was subjected to mechanical grinding and then gas-activated by heating in a CO2 atmosphere at 9000C for 1 hour. Gas activation rather than continued grinding was chosen to minimise particle agglomeration; it produced a 27% weight loss of the carbon, increased the effective surface area, and modified the surface. Titanium dioxide is impregnated into the carbon by mixing an appropriate amount of titanium (IV) isopropoxide with the carbon and allowing it to hydrolyse in air.
Platinum has been dispersed into the gasactivated carbon by reducing chloroplatinic acid with sodium formate solution as described elsewhere. This procedure (yielding comparative electrodes) yields fine platinum particles of uniform size (about 63A diameter) on a carbon substrate.
Chloroplatinic acid solution containing the required proportion of platinum was taken from a 2 weight % stock solution, mixed with half of its volume of carbonate. An appropriate quantity of gas-activated Vulcan XC-72 carbon was added, and the entire mixture was dried in an air oven before it was added, with vigorous stirring, to an excess of boiling 5 weight % sodium formate solution to reduce the chloroplatinic acid to platinum metal. The resulting mass was filtered and washed repeatedly with hot, distilled water before being dried in an air oven.
EXAMPLE 1 Platinum and ruthenium are to be co-deposited, in the atomic ratio Pt:Ru=7:3.
A supported Pt-Ru catalyst was prepared by coimpregnation of the gas-activated Vulcan XC-72 carbon with a mixed solution containing appropriate amounts of chloroplatinic acid H2PtCl6 and ruthenium trichloride RuCI3. The impregnated carbon was evaporated to dryness and reduced at 2000C for 20 hours in flowing H2.
Teflon-bonded electrodes were prepared for electrochemical measurements. The Teflon binder provides the necessary mechanical strength to prevent electrode collapse under the gas pressure required for gas-electrolyte interface control in a gas-diffusion electrode, and it does so while retaining the necessary electrode porosity. The Teflon-bonded electrodes were made as follows: Tetrahydrofuran (THF) was added to a measured quantity of catalysed substrate powder in a beaker, and the mixture was agitated in an ultrasonic bath for about 30 minutes before a few ml of dilute suspension of Teflon emulsion (ICI GP2 Fluon dispersion, particle size 0.1-0.2 microns) was added to the mixture without interruption of the agitation.The product material was centrifuged repeatedly with THF and finally spread on a platinum expanded-metal (Exmet) screen (0.076 mm diameter wire, 1024 mesh cm~2). The coated screen was air-dried for about 15 minutes before it was cold-pressed at 125 kg cm-2 for 5 minutes. The pressed mass was dried for 2 hours at 11 00C and then cured in air at 3600C for 30 minutes. The Teflon content of the electrodes was optimal at 25 to 35% by volume, the content in each case being 30% unless otherwise stated on the Figure. The platinum loading was 3% on Figure 1 and 5% on Figure 2.
The BET surface area of such a substrate was about 600 m2/g and the resistivity about 0.4 ohm cm.
Comparative Pt-Ru electrodes have been made by compressing Pt-Ru electrodes have been made by compressing Pt-Ru alloy onto a platinum mesh at a pressure of 1.7 tonne cm-2.
An electrochemical cell for measuring electrochemical performance parameters was set up containing this substrate as a working electrode, a Hg1Hg2SO6, RH+ reference electrode, a high surface area flatbed counter electrode, and an electrolyte, which was a solution of 2.5H sulphuric acid H2SO4 and 1 M methanol CHsOH in distilled water.
Platinum-black electrodes and platinum dispersed on normal carbon electrodes are easily poisoned.
Howevere, if carbon is treated with CO2 at 900 C, and ruthenium is jointly dispersed with the platinum, good stability and performance are obtained, as may be seen from the Figures.
Interesting features of these figures are significant improvement in performance at higher electrolyte temperature, high current densities, decrease in the otherwise rapid rise in overpotential for the first few mA, and enhanced performance in terms of the electrode design. The poisoning mentioned above is tentatively believed to result from poisoning of platinum itself. This can be slowed, i.e. lifetime can be lengthened, by having fine dispersed platinum particles, hence the preference for in situ chemical formation of the platinum on the substrate.
Meanwhile, the carbon treatment mentioned above gives, as shown, a useful decrease in overpotential.
The combination of decrease in overpotential and longer life is valuable.
Comparison of current-potential curves with the curves of potential versus current per mg of platinum shows that significant reduction in cost is achieved by deposition of the Pt-Ru catalyst onto the activated carbon substrate.
The service-life data for various electrodes are presented in Figure 4.
A power density of about 80 mW cm~2 could be achieved if one were to combine the methanol anode (Pt8Ru/Ct) and an oxygen reducing cathode.
EXAMPLE 2 A platinum/titanium dioxide/treated carbon electrode was made as follows. 400 mg of gas treated Vulcan XC-72 was suspended in 100 ml of water and heated to boiling. A dilute solution of titanium (IV) isopropoxide in isopropanol was slowly added and the solution boiled for 1 hour. The pH was then adjusted to 12 with NH3OH. A 2% chloroplatinic acid solution was then added and after a further hour the solution brought to dryness.
The resulting solid was dried at 1100 for 12 hours, resuspended in water and a five-fold excess of HCOONa added. The mixture was then boiled for 2 hours, filtered, washed with boiling distilled water and dried at 1100.
The electrode was made as described previously for platinised carbon electrodes and had the composition: Pt-7%, TiO2-3%, Cr#63%, Teflon 27%.
EXAMPLE 3 A platinum/ruthenium/titanium dioxide/treated carbon electrode was made as follows. 600 mg of gas treated Vulcan XC-72 was suspended in 100 ml of water and heated to boiling. A dilute solution of Titanium (IV) isopropoxide in isopropanol was slowly added followed by 2% solutions of chloroplatinic acid and ruthenium trichloride in water. The resulting solution was neutralised with a dilute solution of sodium hydrogen carbonate. The slurry was brought to dryness, dried at 1100 for 12 hours, re-suspended in water, reduced with HCOONa, filtered, washed with water and finally dried as above.

Claims (20)

1. An electrode for oxidising methanol, comprising a substrate which is an electronic conductor capable of reducing elemental oxygen to water yielding not more than 5% hydrogen peroxide, to which substrate is attached a catalyst comprising platinum and either one or both of titanium dioxide and ruthenium.
2. An electrode according to Claim 1, wherein the substrate is porous.
3. An electrode according to Claim 1 or 2, wherein the electronic conductor is capable of reducing elemental oxygen to water yielding not more than 1% hydrogen peroxide.
4. An electrode according to Claim 3, wherein the electronic conductor is capable of reducing elemental oxygen to water yielding not more than 0.1% hydrogen peroxide.
5. An electrode according to any preceding claim, wherein the catalyst comprises (i) Pt and Ru; or (ii) Pt and TiO2; or (iii) Pt and Ru and TiO2.
6. An electrode according to any preceding claim, wherein the substrate is carbon of an ash content less than 0.1%.
7. An electrode according to Claim 6, wherein the carbon is 'coconut carbon', which is derived from coconut shells by converting these to charcoal, washing and comminuting the charcoal, and exposing the comminuted charcoal to gas.
8. An electrode according to Claim 7, wherein said gas to which the comminuted characoal is exposed is carbon dioxide or is ammonia or is carbon dioxide followed by ammonia or is steam.
9. An electrode according to Claim 6, wherein the carbon is of poorly crystalline type and has a surface area of at least 200 m3/g, a mean particle size in the range 5 mm to 50 mm, and an apparent density of 80 to 110 kg/m3.
10. An electrode according to Claim 9, wherein the carbon is treated by comminuting it and exposing it to gas at elevated temperature.
11. An electrode according to Claim 10, wherein the carbon before the comminution has a surface area of not more than 300m2/g.
12. An electrode according to Claim 10 or 11, wherein the carbon before the comminution has a pH below 7.
13. An electrode according to any of Claims 10 to 12, wherein the carbon is exposed to only carbon dioxide.
14. An electrode according to Claim 13, wherein the exposure is for 40 to 90 minutes at 800 C to 1000 C.
15. An electrode according to any preceding claim, wherein the catalyst is present in a proportion of from 1 to 15% by weight of the substrate.
16. An electrode according to Claim 15, wherein the catalyst is present in a proportion of from 2 to 12% by weight of the substrate.
17. A method of making an electrode as claimed in any preceding claim, comprising applying a solution containing a platinum and a ruthenium compound onto the substrate and decomposing the compounds, whereby the desired catalyst is precipitated on, and is attached to, the substrate.
18. A method according to claim 17, wherein the substrate is mixed with a titanium compound which is decomposed to form titanium dioxide.
19. A fuel cell wherein methanol is oxidised at an electrode, the electrode being as claimed in any of Claims 1 to 16 or having been made by a method according to Claim 17 or 18.
20. A method of oxidising methanol, comprising contacting methanol and water at an electrode as claimed in any of Claims 1 to 16 or having been made by a method according to Claim 17 or 18, and applying to the electrode a potential more positive than -0.3 volts with respect to the Hg/Hg2SO4 electrode.
GB08704526A 1986-02-28 1987-02-26 Electrode for oxidising methanol Withdrawn GB2187880A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB868604982A GB8604982D0 (en) 1986-02-28 1986-02-28 Electrode for oxidising methanol
GB868622455A GB8622455D0 (en) 1986-09-18 1986-09-18 Electrode

Publications (2)

Publication Number Publication Date
GB8704526D0 GB8704526D0 (en) 1987-04-01
GB2187880A true GB2187880A (en) 1987-09-16

Family

ID=26290416

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08704526A Withdrawn GB2187880A (en) 1986-02-28 1987-02-26 Electrode for oxidising methanol

Country Status (3)

Country Link
EP (1) EP0259424A1 (en)
GB (1) GB2187880A (en)
WO (1) WO1987005445A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9507012D0 (en) * 1995-04-05 1995-05-31 Johnson Matthey Plc Improved electrode

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2095025A (en) * 1981-03-17 1982-09-22 Hitachi Ltd Acid electrolyte fuel cell
GB2164785A (en) * 1984-09-06 1986-03-26 Nat Res Dev Electrode for reducing oxygen

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3212936A (en) * 1960-11-07 1965-10-19 Air Prod & Chem Method of forming paste-form fuel cell electrode
GB1163479A (en) * 1967-03-17 1969-09-04 Engelhard Min & Chem Fuel Electrodes
GB1409260A (en) * 1971-12-29 1975-10-08 Exxon Research Engineering Co Fuel cell having non-alloyed palladium-ruthenium anode catalyst
GB1501102A (en) * 1974-02-19 1978-02-15 Shell Int Research Method for the production of a composite catalyst suitable for use in forming fuel cell electrodes
US3964933A (en) * 1974-04-08 1976-06-22 Exxon Research And Engineering Company Carbon article including electrodes and methods of making the same
US4028274A (en) * 1976-06-01 1977-06-07 United Technologies Corporation Support material for a noble metal catalyst and method for making the same
JPS5679858A (en) * 1979-12-04 1981-06-30 Hitachi Ltd Liquid-penetrable electrode for fuel battery

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2095025A (en) * 1981-03-17 1982-09-22 Hitachi Ltd Acid electrolyte fuel cell
GB2164785A (en) * 1984-09-06 1986-03-26 Nat Res Dev Electrode for reducing oxygen

Also Published As

Publication number Publication date
WO1987005445A1 (en) 1987-09-11
GB8704526D0 (en) 1987-04-01
EP0259424A1 (en) 1988-03-16

Similar Documents

Publication Publication Date Title
US4354958A (en) Fibrillated matrix active layer for an electrode
US4456521A (en) Three layer laminate
US4379772A (en) Method for forming an electrode active layer or sheet
US4500647A (en) Three layer laminated matrix electrode
US4518705A (en) Three layer laminate
US4716087A (en) Platinum-copper alloy electrocatalyst and acid-electrolyte fuel cell electrode using the same
Goodenough et al. Porous carbon anodes for the direct methanol fuel cell—I. The role of the reduction method for carbon supported platinum electrodes
CA1190183A (en) Non-bleeding gas electrode having plural porous layers
EP1169743B1 (en) Gas difffusion substrates
US4440617A (en) Non-bleeding electrode
KR101229400B1 (en) Platinum/ruthenium catalyst for direct methanol fuel cells
Ralbag et al. Composite materials with combined electronic and ionic properties
CN101583420A (en) Porous clusters of silver powder promoted by zirconium oxide for use as a catalyst in gas diffusion electrodes, and method for the production thereof
JP2001085020A (en) Electrode catalyst for fuel cell
KR20060080727A (en) Pt/ru alloy catalyst for fuel cell
CN1317158A (en) Electrochemical oxidation of hydrogen sulfide
US20050282061A1 (en) Catalyst support for an electrochemical fuel cell
CN112002915B (en) Oxygen electrode bifunctional catalyst, preparation method and application
US4337139A (en) Fluorinated carbon electrode
de la Fuente et al. Enhanced methanol electrooxidation activity of PtRu nanoparticles supported on H2O2-functionalized carbon black
Sun et al. Pd–Ru/C as the electrocatalyst for hydrogen peroxide reduction
CA1208168A (en) Producing electrode active layer from active carbon particles and fibrillated polytetrafluoroethylene
US4377496A (en) Gas diffusion electrode and process
GB2187880A (en) Electrode for oxidising methanol
KR100965836B1 (en) Method for preparing metal catalyst comprising fluorine functionalized carbon support

Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)