Measurement of effective oxygen diffusivity in electrodes for proton exchange membrane fuel cells

This paper describes a novel method to measure directly effective diffusivity in electrodes as a function of temperature and relative humidity (RH) at conditions that are relevant for proton exchange membrane fuel cells (PEMFCs). The efficacy of this method to measure effective oxygen diffusivity (DO2eff) is demonstrated with measurements of a series of electrodes of varying the ionomer-to-carbon weight ratio (I/C ratio). The measured DO2eff decreases sharply with increasing I/C ratio from 0.5 to 1.5 at the same RH, and reduces gradually with increasing RH from 0% to 100% at the same I/C ratio. The measured DO2eff is considerably smaller than the calculated one using the Bruggeman correction, indicating the Bruggeman correction drastically underestimates the tortuosity with increasing I/C ratio in PEMFC electrodes.