Proton Generation and Transport in the Fuel Cell Environment: Atomistic Computer Simulations

In: Journal of computer-aided materials design, Jg. 14 (2007) ; Supplement 1, S. 253-258
ISSN: 0928-1045
Zeitschriftenaufsatz / Fach: Chemie
Fakultät für Chemie
Abstract:
Hydrogen atoms in direct methanol fuel cells are produced ’in situ’ by dissociation
of methanol on precious metal catalysts (Pt, Pt/Ru) in an aqueous environment. The
abstraction of the first hydrogen atom via C–H bond cleavage is generally considered to be
the rate-limiting step of dissociative methanol adsorption on the catalyst surface. This oxidation
reaction on platinum particles in a fuel cell is investigated by means of a combined
approach of classical molecular dynamics (MD) simulations and ab initio calculations in
order to obtain an understanding of the role of the solvent for the stabilization of intermediates
and for the enhancement of proton desorption from the catalyst surface and subsequent
transfer into the nearby polymer electrolyte membrane (PEM). The anodically generated
protons need to migrate efficiently through the membrane to the cathode were they are consumed.
At the same time water and methanol (in a direct methanol fuel cell) transport should
be slow. Humidified PEMs are considered to consist of a nanometer-scale phase-separated
bicontinuous network of polymer regions providing structural integrity, and of aqueous regions
providing the pathways for proton conduction. MD simulations provide a powerful
theoretical tool for the investigation and clarification of the relationship between molecular
structure and these transport phenomena. In order to atomistically model larger fractions of a
humidified PEM, a coarse-grained model of humidified polymer electrolyte membranes has
been developed.