Measurements of Effective Oxygen Diffusivity, Pore Size Distribution, and Porosity in PEM Fuel Cell Electrodes

Abstract

This paper presents the measurement results of effective oxygen diffusivity (DO2), pore size distribution, and porosity of proton exchange membrane fuel cell (PEMFC) electrodes, and the calculated tortuosities using these measurement results. A novel method has been developed to directly measure effective oxygen diffusivity in electrodes as a function of temperature and relative humidity (RH) on a conventional PEMFC platform with 50 cm2 flow fields. The pore size distributions and porosities of catalyst powder and electrodes are measured by nitrogen adsorption with the BJH model and mercury intrusion porosimetry (MIP). The measured porosities from the MIP results are considerably less than those calculated from material densities, suggesting that ionomer blocks some pores in electrodes. The calculated tortuosities are larger than those predicted by Bruggeman correction, indicating the Bruggeman correction underestimates the tortuosity and thus overestimate effective DO2 in PEMFC electrodes.