By using the finite element method two cases are treated for which inhomogeneous current distributions and their frequency dependence is of crucial importance: (i) the impedance of different microstructures is calculated and compared with the brick layer model; (ii) the interplay of current constriction at the three-phase boundary and the electrode polarization of porous gas electrodes as used in solid oxide fuel cells (SOFC) is investigated. The impact for a quantitative equivalent circuit analysis is discussed.