In Direct Methanol Fuel Cells (DMFC), methanol is directly oxidized into hydrogen without any bulky and expensive reformer, leading to lower cost and more compact systems.
This project aims to conceive and to develop new catalytic electrodes prepared by dispersion of a catalytic material in a convenient substrate. The objectives are to design a DMFC with good performances (200 mA/cm2 at a cell voltage of 0.5 V and a temperature of 80(C) with a low Pt loading ( < 1 mg/cm2).
Previous fundamental work, carried out during past CEC programmes (EN3E-0071-F and JOUE-CT90-0037) led to a better knowledge of the reaction mechanisms of methanol oxidation. Therefore new catalytic electrodes were conceived in order to improve the electroactivity (decreasing of the oxidation overvoltage), the reaction selectivity (towards a complete oxidation to CO2) and the long term stability (decreasing of self poisoning by adsorbed CO).
Different platinum based electrodes will be prepared on different conducting substrates, and characterized both for their structure and composition by physicochemical methods, and for their electrocatalytic activity towards methanol oxidation by electrochemical methods. Pt and Pt alloys (Pt/Ru, Pt/Sn, Pt/Ru/Sn, ...), which were shown to be good electrocatalysts for methanol oxidation, will be deposited, on a ionomeric membrane (Nafion or similar membranes), by chemical reduction of the metallic salts (University of Poitiers). On the other hand, Pt and Pt alloys (Pt/Ru, ...) highly dispersed on a carbon substrate (carbon felt, carbon weave, ...), will be obtained by radiolytic decomposition of the corresponding salts. Particle size and dispersion, and alloy composition, will be determined by electron microscopies, and X-fluorescence microanalysis, either in Poitiers (SEM), or in Orsay (TEM, HRTEM), or in CREMGP of Grenoble (TEM). Determination of the true surface area, and of the electrocatalytic activity, will be carried out by cyclic voltammetry (University of Alicante, University of Poitiers).
The intermediate species and reaction products of methanol oxidation will be investigated "in situ", using Infrared Reflectance Spectroscopies, such as EMIRS and FTIRS (Poitiers).
Model electrodes, consisting of Pt single crystals (vicinal and stepped surfaces) modified by the irreversible adsorption of metal adatoms (Bi, Ru, ...), will be prepared at CNRS-Bellevue and characterized by voltammetry (Bellevue and Alicante) and by Scanning Tunnelling Microscopies (Alicante). On the other hand, the effect of foreign metal adatoms on the adsorption of carbon monoxide CO (resulting from CH3OH dissociation) or of methanol will be investigated by UHV techniques (LEED, XPS, TDS) at the University of Southampton.
The study of oxygen cathodes with a low Pt content will be mainly carried out at CREMGP-Grenoble. Carbon substrates (eg. Vulcan XC-72) and ionomeric membranes (eg. Nafion 117) will be considered. The electrocatalytic activity for oxygen reduction, and selectivity towards methanol oxidation, will be achieved by platinum alloys (Pt/Au, Pt/Pd, Pt/Ru, ...). The electrode structure (pore size, thickness of the active layer, proportion of Nafion, ...) will be optimized by mathematical modelling of the gas diffusion electrode (Grenoble).
A complete methanol fuel cell, with a significative size (electrode area 10 cm2) will be assembled in Poitiers, in order to test the catalytic electrodes and to determine the overall characteristics of the fuel cell (polarization curves, energy efficiency, power density, long term stability).
Funding SchemeCSC - Cost-sharing contracts
SO17 1BJ Southampton