  Impedance of all oxygen transport processes in PEM fuel cell has negative
real part in some frequency domain. A model function (kernel) for calculation
of distribution of relaxation times (DRT) of a PEM fuel cell is suggested. The
kernel is designed for capturing impedance with negative real part and it stems
from the equation for impedance of oxygen transport through the gas--diffusion
transport layer (doi:10.1149/2.0911509jes). Using recent analytical solution
for the cell impedance it is shown that DRT calculated with the novel $K_2$
kernel correctly captures the GDL transport peak, while the classic DRT based
on the $RC$--circuit (Debye) kernel misses this peak. Employing $K_2$ kernel,
analysis of DRT spectra of a real PEMFC is performed. The leftmost on the
frequency scale DRT peak represents oxygen transport in the channel, and the
rightmost peak is due to proton transport in the cathode catalyst layer. The
second, third and fourth peaks exhibit oxygen transport in the GDL, faradaic
reactions on the cathode side, and oxygen transport in the catalyst layer,
respectively.
