We report a physics-based model for impedance of the cathode catalyst layer (CCL) with nonuniform Nafion loading in a PEM fuel cell. The general system of equations for the perturbation amplitudes is derived and solved analytically for the cases of either fast oxygen transport, or fast proton transport in the CCL. The expressions for the respective CCL impedances are obtained. In the case of large cell current, we analyse the numerical solutions for the CCL impedance. (C) 2017 Elsevier B.V. All rights reserved.