The Ruddlesden‒Popper phases pertain to numerous promising materials with the mixed ionic-electronic conductivity used in devices such as oxygen-conducting membranes, solid oxide fuel cells (SOFC), and electrolyzers, which operate in the intermediate temperature region. Their high total conductivity and oxygen mobility make these materials candidates for the mentioned applications. The structure, the oxygen mobility, and the electrochemical characteristics of the promising materials La1.7Ca0.3Ni1 – xCuxO4 + δ (x = 0–0.4) are studied. According to the high-precision XRD data, all synthesized materials are single-phased and have the tetragonal structure. The unit cell parameter c and the cell volume increase upon doping with copper. The content of overstoichiometric interstitial oxygen decreases with doping and the compositions with the high copper content become oxygen deficient. The samples are characterized by the nonuniform oxygen mobility. By and large, the trend for the decrease in the oxygen mobility with the increase in the Cu content is observed in the series of La1.7Ca0.3Ni1 – xCuxO4 + δ samples. By impedance spectroscopy studies, it is shown that the electrodes with the La1.7Ca0.3Ni1 – xCuxO4 + δ functional layers with the copper content x > 0.2 have a higher electrochemical activity. The factors responsible for the efficiency of electrodes are analyzed. The results obtained in this study demonstrate that La1.7Ca0.3Ni0.6Cu0.4O4 + δ materials are the candidates for the air electrodes in electrochemical devices.