Solid oxide fuel cells have been one of the most promising alternatives to fossil-fuel based energy in the past few years. One of the most important challenges is increasing the performance of mixed ionic-electronic conducting cathodes at lower temperatures. One such cathode which has been studied lately is based on the Ruddlesden-Popper phase La2NiO4 with Sr and Mn replacements on the A and B sites respectively. Using electrochemical impedance spectroscopy and distribution of relaxation time analysis this paper attempts to separate the different processes in such cathodes. Three different processes were identified with a low, medium, and high frequency. The three processes were related to three different processes respectively: oxygen diffusion, oxygen surface exchange and charge transfer, and finally oxygen transfer through the electrode/electrolyte interface.