Characterizing Local O2 Diffusive Losses in GDLs of PEFCs Using Simplified Flow Field Patterns (“2D”,“1D”,“0D”)

Abstract

By means of advanced diagnostic tools – neutron imaging, pulsed gas method (helox or O2 pulses during air operation) and electrochemical impedance spectroscopy (EIS) – three different flow fields are characterized in a differential (small-size cell operated at high stoichiometry) Polymer Electrolyte Fuel Cell (PEFC) to emulate the local behavior of a full-size cell. The channel-rib structures are designed so as to obtain 2D, 1D and 0D gradients of O2 concentration across the gas diffusion layer (GDL). The important bulk-diffusion losses (evaluated with pulsed helox) of the “2D” cell compared to the “1D” cell indicate the effect of lateral oxygen diffusion in the GDL. Non-bulk diffusion losses (Knudsen and/or thin film diffusion, evaluated with pulsed O2) also play a non-negligible role on the overall diffusive losses. In particular, their increase in dry conditions for the “1D” and the “0D” cells might be a consequence of drying effects in the electrode.EIS spectra can be interpreted consistently with the results of the pulsed gas method: the increase of arc diameter can be correlated with the overall mass transport losses including both bulk and non-bulk diffusion losses.