Impedance Spectroscopy Characterization of Oxygen Transport in Low– and High–Pt Loaded PEM Fuel Cells

Abstract

© The Author(s) 2017. We report fitting of the physics-based model for the cathode side impedance to the experimental spectra of low-Pt loaded (0.1/0.1 mgPtcm-2) and high-Pt loaded (0.4/0.4 mgPtcm-2) PEM fuel cells measured in the range of current densities from 50 to 400 mA cm-2. Fitting allowed us to separate the oxygen diffusion coefficients in the catalyst layer Doxand in the gas-diffusion layer Db, and the respective mass transfer coefficients of the electrodes of both types. In the low-Pt electrode, Doxis an order of magnitude lower, than in the high-Pt electrode; however, due to 4-fold difference in the electrode thickness, the respective mass transfer coefficients are close to each other. In both the electrodes, the oxygen diffusion and the mass transfer coefficients in the GDL are nearly the same and they are much higher, than the respective coefficients in the CCLs. The ORR Tafel slope and Doxexhibit linear growth with the cell current density; both effects could be attributed to "cleaning" of Pt surface from oxides at lower cell potential.