The CO tolerance of commercial Pt and PtRu anode electrodes from different suppliers (E‐Tek and Tanaka) has been examined in polymer electrolyte fuel cells (PEFC) using AC‐impedance spectroscopy along steady‐state current‐voltage curves. A simple mathematical model has been derived in order to extract important kinetic parameters for CO poisoning on different anode electrodes. The Tanaka PtRu (40:60) electrode demonstrated the best CO tolerance under the selected operating conditions.Inductive behavior in the low frequency region of the impedance spectra for the E‐Tek Pt and PtRu electrode proved to be characteristic for CO poisoning. However, the impedance spectra of the Tanaka PtRu electrode did not show any inductive behavior and its CO surface coverage, extracted by fitting the experimental data to the model, was lower than the surface CO coverage of the E‐Tek electrodes.
The commercial success of the polymer electrolyte fuel cell (PEFC) will to a large extent be determined by the nature, properties, functionality, and cost of the electrochemical sub-components used in the membrane electrode assembly (MEA). Materials research activities in Switzerland for the PEFC are being pursued at the Paul Scherrer Institut (Villigen AG) and the Swiss Federal Institute of Technology in Lausanne with different objectives. The radiation grafted proton exchange membrane developed at the Paul Scherrer Institut (PSI) has been brought to a near-product-like quality level with encouraging performance close to state-of-the-art materials and a life-time of several thousand hours. Furthermore, the membrane shows low methanol crossover in the direct methanol fuel cell. In addition, polyarylene block copolymer membranes have been investigated as an option for fluorine-free membranes. The electrocatalysis of Pt in acidic solution and in contact with a solid electrolyte, the development of new methanol oxidation and oxygen reduction catalysts, and co-sputtering of Pt and carbon as an alternative method for catalyst preparation are areas of fundamental research. More applied research is performed in the characterization of commercial electrodes in single cells, using standard as well as advanced diagnostic tools developed in-house. This article gives an overview over the research and development projects in Switzerland related to materials and components for the PEFC.
The nanostructures of co-sputtered Pt/C layers were investigated by anomalous small-angle X-ray scattering (ASAXS) experiments with synchrotron radiation. The ASAXS method permits us to separate the platinum-scattering contribution from the carbon background and thus opens up the possibility to retrieve nanostructures formed by the Pt atoms. To obtain the structural information from the scattering data, a columnar structure model is proposed and applied to three different samples prepared with different platinum sputter targets. The results are compared to those obtained from cyclic voltammetry.
Fundamental aad phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against expedmetrts. Computationally efficient models suited for eDgineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method CVAM) that considers only the lùmped effect of pre-selected system comporents. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC ald the latter was used for the optimization of commercial SOFC systems. State Space Modeting (SSM) was used 10 identiry the main reaction pathways in SOFC and, in conjunction with the implemertatior of geometrically well-defined electrodes, has opened a new direction for the understarding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the CO-poisoning-induced aûode impedance in PEFC.Detâiled nùmerical models such as the Lattice Boltzmarn (lB) method for tuaûsport in porous media and the fulI 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can implove the understanding of the rçlated phenomena, a necessary condition for the developmert of both appropriate simplifred models as well as reliable technologies.Within the LB ïiamework, a technique for the charactedzation and computer-recoDstmction of the porous electrode sfuùcture was developed using advanced pattem recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with intemal mgthare steam reformitrg and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been pùt forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional reclangular shaped units. Themo-economic modeling for the optimization of PEFC is finally addressed Kelvords: multidimensional simulations of fuel cells; porous electrode stucture chaÉcterization; state-spâce modeling of electrochemical reactions; thermo-economic o?timization
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