A model for impedance of a PEM fuel cell cathode with poor electron conductivity

A model for impedance of the cathode catalyst layer (CCL) with poor electronic conductivity σe is developed. In the case of small cell current, an analytical expression for the CCL impedance is derived. At small currents, finite σe increases the static cell resistivity by the value 1/(3σe). In addition, the CCL exhibits a pure ohmic resistivity, which is equivalent to proton and electronic resistivities connected in parallel. Finite σe distorts the shape of the Nyquist spectrum in the HF domain; the CCL proton conductivity σp can no longer be determined simply as a projection of the straight HF line onto the real axis. However, σp and σe can be found by fitting the model equations to the experimental spectra.