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Optimization of electrocatalysts for a direct methanol fuel cell

Objective

Fuel cells usually need hydrogen as a fuel to produce electricity. An alternative fuel is methanol, although the use of methanol requires an expensive, bulky reformer. Direct-methanol fuel cells (DMFC) offer the possibility of oxidising methanol directly, leading to lower cost and a more compact system.

This project will develop and validate a DMFC with methanol being continuously supplied in gaseous phase from a tank. The electrolyte will be a polymer membrane like Nafion 117 or a solid state membrane. This research should lead to a current density of 500 mA/cm2 at 0.6V, with a Pt catalyst load of 1mg/cm2.
Active PtRu- and Pt-catalysts have been prepared, based on colloidal deposition from sulphito complexes, Nafion-bonded on carbon support. The problem of ohmic resistance has been partially overcome by improved cell and electrode design. Operating with a vapour feed 50:50 MeOH:Water and oxygen at 80 degrees C a power density of 0.17W/cm{2} at 300mV was obtained. The fuel utilisation was found to be 0.56 at 550mV and 75mA/cm{2}. Influence of Nafion on methanol chemisorption was investigated (Newcastle).

The role of the second metal (Ru, Sn, W, Ni) next to Pt on the rate of methanol adsorption and oxidation has been studied. W and WC used in immersed electrode versions showed an improved catalytic activity, comparable to Ru. With a good lateral conductivity of the catalytic layer and a respective design of the electron collector, the double layered structure of electrodes on PEM can be made redundant. A technique for ultra-thin electrode preparation has been developed (Sofia).

Methanol anodes via the Sulfito Complex Method were compared with those prepared by the Formate Reduction Method. The electrochemical codeposition of Pt and Ru was investigated in detail, e.g. with the help of rotating electrodes also. The currents for Pt- and Ru deposition during a codeposition procedure do not depend linearely on metal concentrations. Low noble metal anodes have been checked in EMA's, the methanol crossover being determined via cyclic voltammograms as 50mA/cm{2} at 90 degrees C, in agreement with results from International Fuel Cells (IFC). CO and methanol oxidation are discussed as function of PtRu catalyst composition and temperature. Characterization of catalysts was made via in-situ FTIR, TDS, Cyclic Voltammetry and DEMS (Bonn).

In long time performance, oxygen cathodes (from Bonn) in H2SO4 electrolyte at 60 degrees C show good stability over 300 hrs. Methanol electrodes (from Bonn and Newcastle) performed well initially, but than decayed in an unexpected fashion (Cork).

Different carbon materials as used for catalyst support were studied via thermal analysis. Decomposition products are CO2 and small amounts of hydrocarbons. Carbon-oxygen compounds at the surface obviously determine the properties. Vulcan XC72 performed better than Printex XE2 (Ulm).
- Optimization of binary and ternary alloy catalysts for methanol, study of particle size and surface composition, corrosion of dispersed alloys (Newcastle)
- 3-phase zone optimization at polymer membrane surfaces, optimization of metal deposition method, UHV adsorption of methanol, CO at different metal surfaces (Bonn)
- Methanol diffusion through solid state membranes, 3 phase zone construction of solid state material (Ulm in cooperation with Innovision) - Degradation of electrocatalysts for methanol and oxygen, long time performance of single electrodes (Cork)
- Catalysts analysis, corrosion of carbon support (Ulm)
- Preparation and test of methanol anodes and oxygen cathodes (Bonn, Newcastle)
- Test of complete Membrane Electrode Assemblies (Bonn, Ulm).

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Rheinische Friedrich-Wilhelms-Universität Bonn
Address
Römerstraße 164
53117 Bonn
Germany

Participants (3)

CENTER FOR SOLAR ENERGY AND HYDROGEN RESEARCH BADEN-WÜRTEMBERG
Germany
Address
Hessbruehlstrasse 21C
70565 Stuttgart
UNIVERSITY COLLEGE CORK, NATIONAL UNIVERSITY OF IRELAND, CORK
Ireland
Address
College Road
30 Cork
UNIVERSITY OF NEWCASTLE UPON TYNE
United Kingdom
Address
Kensington Terrace 6 Bedson Building
NE1 7RU Newcastle Upon Tyne