  A model of PEM fuel cell impedance is developed taking into account imposed
harmonic perturbation of the air flow velocity in the cathode channel. The flow
velocity modulation with the amplitude proportional to AC amplitude of the cell
potential lowers the resistivity $R_h$ due to oxygen transport in channel. When
relative amplitudes of velocity and potential oscillations are equal, a
complete compensation of $R_h$ occurs. This effect explains experimental
findings of Kim et al. (doi:10.1016/j.jpowsour.2008.06.069) and Hwang et
al.(doi:10.1016/j.ijhydene.2010.01.064), who demonstrated significant
improvement of PEM fuel cell performance under oscillating air flow velocity.
