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Proton Transport in Material for Fuel Cell Application

For power applications, such as fuel cells, the polymer electrolyte membrane fuel cell (PEMFC) has been considered a promising alternative energy converter. The most commonly used membrane is Nafion®. This polymer electrolyte membrane requires hydration for best performance. Therefore, its application is usually limited to ambient pressure and temperatures below the boiling point of water.

Within the DFG Priority Program 1181, our group in cooperation with experimental groups investigates membranes operating at elevated temperatures up to about 450 K and under dry conditions.

Research work focuses on the development of new bi-functional inorganic particles, such as functionalized Si-MCM-41 (Fig.A) or periodic mesoporous organosilicates (PMO, Fig.B). These serve as water reservoir as well as proton conductors after homogeneous incorportion into mechanically stable and proton-conducting high-temperature resistant polysiloxane membranes.

The modeling work has two main purposes. First, to clarify the structural requirements of the proton conductor and the water management in the inorganic particles. Second, to analyze the mechanism of the proton transport under varying environmental conditions.

The project is developed via the application of different computational methods as density-functional based tight-binding method (DFTB), potential of mean force calculation (PMF), quantum mechanics/molecular mechanics coupling (QM/MM), classical molecular dynamics (MD) and Monte Carlo simulations (MC).

in Detail:

The performance and properties of different alkane-sulfonic acid and alkane-imidazole proton conducting groups has been studied in isolated systems under dry conditions. In first step, the proton transport was analyzed using a simple pair interaction picture (energy barrier calculations for the proton transport and radial distribution function (RDF) for the dynamic of the groups). This study showed the dependence of proton transport on various properties, such as temperature, length of the alkane chain (spacer length) and density of conducting groups per area, which could be affirmed by experimental research.

Via QM/MM coupling, MD simulations of such system taking all interactions and proton transport into account were performed. The trajectory of the excess proton is observed using the modified center of excess charge coordinate (mCEC) and the self-diffusion coefficient was calculated.

Another important issue is the influence of the SiO2 host materials (Si-MCM-41 or PMO) and water molecules on the proton transport.

Therefore, the potential of mean force (PMF) for the proton transport in the presence of water is calculated and MD simulation are run simulating the water distribution inside a functionalized SiO2 pore.

Support

DFG SPP-1181 "Nanoskalige anorganische Materialien durch moleculares Design: Neue Werkstoffe für zukunftsweisende Technologien" (2006 - 2012)

DAAD " Proton transfer in conductor materials for fuel cell applications " (2009)

Investigators

  • Dr. Christof Köhler
  • Dr. Pia Tölle
  • Diego Fernando Portaluppi (2008)
  • Dr. Welchy L. Cavalcanti (2006-2008)

Cooperations

  • Prof. G. Seifert (Dresden)
  • Prof. M. Santos and Prof. Wagner Figueiredo  (Santa Catarina, Brazil)
  • Prof.  G. Grathwohl (Bremen)
  • Dr. Volker Weiß (BCCMS)
  • Dr. Welchy L. Cavalcanti (IFAM, Bremen)
  • Dr. M. Hoffmann (IFAM, Bremen)