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BASIS FOR THE DESIGN OF AN ELECTROCATALYTIC ANODE FOR AN ACID METHANOL FUEL CELL. INVESTIGATION OF THE SELECTIVITY OF METALLIC CATALYSTS FOR THE ELECTROOXIDATION OF METHANOL.

Objective

UNDERSTANDING OF THE REACTION MECHANISM OF METHANOL ELECTROOXIDATION USING WELL DEFINED PLATINUM ELECTRODES (SINGLE CRYSTALS, POLYORIENTED SURFACES, FINELY DIVIDED SURFACES, SURFACES MODIFIED BY FOREIGN SPECIES, IN PARTICULAR METALLIC ATOMS).

KNOWLEDGE OBTAINED ABOUT THE MOLECULAR MECHANISM OF THE REACTION UNDER THESE CONTROLLED CONDITIONS WILL ENABLE A MORE PRECISE EVALUATION OF THE REAL LIMITS TO THE OPTIMUM PERFORMANCE OF A METHANOL ANODE AND LEAD TO THE DESIGN OF MORE EFFICIENT AND SELECTIVE CATALYSTS.
The design of an electrocatalytic anode for an acid methanol fuel cell has been studied. The electrochemical study of the blocking species formed and accumulated on the basal orientations, and on a set of stepped surfaces, have given evidence for the structure sensitive character of the poisoning reaction. This study lead to the conclusion that adsorbed carbon monoxide is the stable long term product, linearly or bridge bonded to the surface sites. Determination of the intrinsic activity of an electrode with a given crystalline surface structure requires the use of a special technique. Pulsed voltammetry has been designed for this, with the aim of preserving the ordered surface structure against damage. The intrinsic activity measurements give an estimate of any activity change induced by different means. The effect of adatoms, adsorbed irreversibly, on the formation and accumulation of the blocking species has been studied thoroughly as well as the effect on its oxidation.
THE R&D WORK PROPOSED IS FOR BASIC RESEARCH INTO THE MECHANISM OF METHANOL OXIDATION WHICH WILL BE CARRIED OUT IN THREE CENTRES: BELLEVUE, POITIERS, SOUTHAMPTON.

SINGLE CRYSTALS PLATINUM ELECTRODES WILL BE MADE, ORIENTED, CUT, POLISHED AND THEIR WORKING SURFACE PREPARED FOR ELECTROCHEMICAL STUDY IN BELLEVUE AND MADE AVAILABLE TO THE OTHER TWO PARTICIPANTS.

ELECTROCHEMICAL CHARACTERIZATION OF THE ELECTRODE SURFACES WILL BE DONE IN EACH LABORATORY AT THE TIME OF EACH EXPERIMENT FOLLOWING THE STANDARD METHODS DEVELOPED IN BELLEVUE. ON THIS BASIS MODIFICATIONS CAN BE MADE, FOR EXAMPLE BY THE DEPOSITION OF ADATOMS. AT THE SAME TIME SUCH EXPERIMENTS WILL BE USED TO CHARACTERIZE MORE COMPLEX SURFACES: POLYCRYSTALLINE; FINELY DIVIDED.

THE OVERALL REACTION WILL BE CHARACTERIZED USING HPLC AND GC SINCE IT IS OF PRIMARY IMPORTANCE TO KNOW THE EFFICIENCY OF FORMATION OF CO2 AND UNDESIRABLE SIDE PRODUCTS HCHO, HCOOH, ETC...

INTERMEDIATES IN THE REACTION WILL BE STUDIED WITH TWO AIMS:
- TO DEFINE THE COURSE OF THE REACTION AND
- TO FIND CONDITIONS UNDER WHICH THE FORMATION OF BLOCKING INTERMEDIATES IS SELECTIVELY INHIBITED.
ELECTROCHEMICAL STUDIES WILL BE CARRIED OUT IN ALL THREE LABORATORIES, BUT THOSE IN SOUTHAMPTON WILL BE COMBINED WITH EX-SITU ELECTRON SPECTROSCOPY WHILE IN-SITU IR SPECTROSCOPY WILL BE USED MAINLY IN POITIERS.

SURFACE REACTIONS LIKE METHANOL OXIDATION ARE KNOWN FROM PREVIOUS WORK OF THE PROPOSERS TO BE HIGHLY STRUCTURE SENSITIVE. SUCH SYSTEMS HAVE BEEN WIDELY STUDIED IN HETEROGENOUS CATALYSIS, BUT NOT IN ELECTRO-CHEMISTRY. THIS PROBLEM WILL BE ATTACKED BY USING ELECTRODES OF KNOWN STEP STRUCTURE, WHICH WILL EVENTUALLY PERMIT THE UNDERSTANDING OF MORE COMPLEX ELECTRODE SURFACES. ELECTROCHEMICAL ASPECTS WILL BE STUDIED IN BELLEVUE WHILE SPECTROSCOPIC STUDIES WILL BE MADE ON THE SAME ELECTRODES IN SOUTHAMPTON. THE NOTORIOUS DE-ACTIVATION OF ELECTRODES, WHICH REMAINS POORLY UNDERSTOOD WILL BE INVESTIGATED. IT IS ALREADY EVIDENT THAT THIS ARISES FROM TWO CAUSES:
- CHANGE IN THE CRYSTALLINE STRUCTURE OF THE METAL SURFACE AND
- FORMATION OF UNDESIRABLE SPECIES ON THE SURFACE.

THE FORMER WILL BE INVESTIGATED UNDER ELECTROCHEMICAL CONDITIONS WHILE THE LATTER WILL BE STUDIED BY IN-SITU IR SPECTROSCOPY. ELUCIDATION OF THIS PROBLEM WILL ENABLE THE INTRINSIC ACTIVITY OF ELECTRODES UNDER WORKING CONDITIONS TO BE EVALUATED.

THE NATURE OF THE ACTION OF ADATOMS AND SIMILAR SURFACE MODIFIERS WILL BE INVESTIGATED AS A FUNCTION OF SURFACE CEYSTAL STRUCTURE USING THE FULL RANGE OF TECHNIQUES MENTIONED ABOVE, AND WITH EQUALLY FULL COOPERATION BETWEEN THE THREE LABORATORIES. OTHER ELECTRODE MATERIALS SUCH AS ALLOYS SUPPLIED BY OTHER CONTRACTORS WILL BE EXAMINED BY THE SAME METHODS IF THESE MATERIALS ARE SUPPLIED IN SUITABLE FORM.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Centre National de la Recherche Scientifique (CNRS)
Address
1 Place Aristide Briand
92195 Meudon
France

Participants (2)

UNIVERSITE DE POITIERS
France
Address

Poitiers
UNIVERSITY OF SOUTHAMPTON
United Kingdom
Address
Southampton Ocenagraphic Centre, European Way
SO14 3ZH Southampton