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Conception and realization of new catalytic anodes and cathodes for a direct methanol fuel working in acid medium

Objective

Conceive and realize electro-catalytic anodes (methanol electrode) and cathodes (air electrode) for a direct methanol fuel cell
Dispersed platinum and platinum-based alloy electrodes were prepared by different reduction methods (chemical, radiochemical, and electrochemical) of the corresponding metallic salts on different conducting substrates (carbon substrates, conducting polymer, ionomer membranes,...). The chemical reduction technique was improved and new ionomer membranes, leading to improved performances, were considered. The electrode catalysts were characterised both for their physicochemical properties (particle sizes, dispersion, morphology, alloy composition) by electron microscopies (SEM, TEM, STM, AFM), and for their electrocatalytic properties towards either the oxidation of methanol, or the reduction of oxygen, by cyclic voltammetry and steady state polarisation measurements. The way of methanol supply was considered, and the performance with gaseous methanol supply appeared very promising.

Model electrodes, Pt(hkl) single crystals with various steps and terraces, and Pt(hkl) single crystals modified by Ru adatoms irreversibly adsorbed, allowed a better understanding of the role of the surface structure in the reaction mechanism of methanol oxidation. Ruthenium was recognised to be the best promoter of platinum activity. Infrared Reflectance Spectroscopic Techniques confirmed the role of adsorbed CO as poisoning species, and led to the identification of intermediate species and reaction products (such as CO2) of methanol oxidation, as a function of the electrode potential.

Platinum alloys (Pt/Ti, Pt/Au, Pt/Pd) dispersed on a carbon substrates (Vulcan XC-72) were prepared by electrochemical reduction and tested for their activity towards oxygen electroreduction, and for their selectivity towards methanol oxidation. Pt/Au alloys gave the best results for oxygen reduction, but at the expenses of a bad selectivity oxygen/methanol. Modelling of oxygen cathodes consisting of an active layer of a Pt/C catalyst and Nafion suspension led to optimised structures for the reduction kinetics controlled by diffusion limitations.
Fuel cells predominantly oxidize hydrogen to produce electricity. If other fuels such as methane or methanol are used they first have to be converted into hydrogen with a reformer, which is expensive and bulky. This is a serious drawback for applications in transportation. Direct methanol fuel cells are therefore being developed which oxidize methanol directly and which don't require costly external reformers. The main problem is here the poisoning of the catalyst. In past EC R&D new ternary alloy catalysts have been developed which allow operation for 4000 hrs without poisoning of the catalyst, ongoing work is now focused on increasing the current density and reducing the cost. This work is carried out in four coordinated contracts: JOUE-CT89-0011, JOUE-CT90-0026, JOUE-CT89-0007 and its follow-up JOUE-CT90-0037. Both last contracts form one project which is described in a single abstract.

Work on the development of the methanol anode includes the study of reaction mechanisms of methanol oxidation (e.g. formation of intermediate compounds, effect of catalytic single crystal orientation) to decrease the poisoning of the catalyst (University of Alicante and CNRS Bellevue) and the improvement of bimetallic and trimetallic catalyst systems and development of techniques to deposit the catalysts on a convenient substrate (University of Poitiers).

Basic research on air cathodes is carried out by the CREMPG of Grenoble to improve the reaction rates at these electrodes. Pt and Pt alloy catalysts is used on Nafion or carbon substrate.

Methanol and air electrodes is developed by CLAL on the basis of fundamental R&D carried out by the four university laboratories. A novel method is used for the dispersion of the catalysts on the substrate (carbon felts, carbon papers or platinized titanium foils).

In the extension R and D moves from basic R and D on electrodes to the realization of practical electrodes. On the basis of fundamental research carried out by the four university laboratories the best electrode structures and compositions will be selected so that the COMPTOIR LYON - ALEMAND - LOUYOT can develop practical electrodes.

Coordinator

UNIVERSITE DE POITIERS
Address
Rue De Blossac 15
86034 Poitiers
France

Participants (4)

Centre National de la Recherche Scientifique (CNRS)
France
Address
1 Place Aristide Briand
92195 Meudon
Comptoir Lyon Alemand Louyot
France
Address
13 Rue De Montmorency
75139 Paris
INSTITUT NATIONAL POLYTECHNIQUE DE GRENOBLE
France
Address
46 Avenue Felix Viallet
Grenoble
UNIVERSITY OF ALICANTE
Spain
Address
99,Carretera De San Vicente S/n
03080 Alicante