Cathode Stoichiometry Research Articles

In Situ Current Distribution Measurements in Polymer Electrolyte Fuel Cells

There has been much recent interest and development of methods to accurately measure the current distribution in an operating polymer electrolyte fuel cell (PEFC). This paper presents results from a novel technique that uses a segmented flow field with standard, nonaltered membrane electrode assemblies and gas diffusion layers. Multiple current measurements are taken simultaneously with a multichannel potentiostat, providing high-resolution temporal and spatial distribution data. Current distribution data are shown that display the distributed effects of cathode stoichiometry variation and transient flooding on local current density. It is shown that the time scale for liquid accumulation in gas diffusion layer pores is much greater than that of any electrochemical or gas-phase species transport process. In order to facilitate state-of-the-art PEFC model validation, an idealized single-pass serpentine flow field was used, and the exact geometry is presented. © 2003 The Electrochemical Society. All rights reserved.

La2Zr2O7 Formation Between Yttria-Stabilized Zirconia and La0.85Sr0.15MnO3 at 1373 K

AbstractOxygen ion conducting yttria-stabilized zirconia and perovskite-type Sr-doped LaMnO3 have been widely used as solid electrolyte and cathode materials in solid oxide fuel cells. The electrochemical properties of the cathode depend largely on the nanostructure and the phase composition of the interface between cathode and electrolyte. Interfaces between single crystals of 9.5mol% Y2O3-stabilized ZrO2 and porous La0.85Sr0.15MnyO3 (y = 0.95…1.10) were investigated. Atomic force microscopy was used for interface studies of YSZ single crystals after removal of sintered perovskite cathodes. High resolution transmission electron microscopy, electron diffraction and electrochemical impedance spectroscopy were employed for interface characterization. Pyrochlore-type lanthanum zirconate formed at the interface during sintering at 1100°C. Nucleation, growth kinetics, and morphology were largely depending on cathode stoichiometry. Lanthanum zirconate formation was retarded in case of A-site deficient perovskite.