## 1 Introduction  
Sustainable energy is currently one of the fastest growing areas in the field of applied scientific research [1]. The priority tasks for modern energy harvesting and producing technologies include searching for available renewable energy resources in different climate zones of the world [1,2], developing new ways to produce clean energy, such as hydrogen energy [3], solar energy [4], geothermal energy [5], wind energy [6], and bioenergy [7,8], and designing power devices with insitu direct conversion of the various types of energy into electricity in order to lower energy losses [9, 10, 11]. Solid oxide fuel cells (SOFCs) are well-known devices used for the direct conversion of chemical reaction energy to electric power [12, 13, 14]. The advantages of SOFCs include the minimal content of noble metals required for their components [15] and their compactness and fuel flexibility [16]. Among the disadvantages of the traditional SOFCs when operating at high working temperatures (900 \({}^{\circ}\)C and higher) are the significant chemical interaction between the SOFC's functional layers and the rapid aging of the materials [17], with consequential fast deterioration in the cells' power characteristics [18]. However, attempts to reduce the operating temperatures have led to a drastic increase in ohmic losses related to the temperature-activated nature of the solid-state electrolyte conductivity. This facilitated the search for electrolytes capable of operating effectively in the intermediate temperature range, such as, for example, oxygen-ion-conducting electrolytes based on CeO\({}_{2}\) and Bi\({}_{2}\)O\({}_{3}\)[19,20], Sr, Mg-doped LaGaO\({}_{3}\)[21], and proton-conducting BaCe(Zr)O\({}_{3}\) electrolytes [22,23]. The most pronounced factors contributing to the IT-SOFC performance deterioration are the slow kinetics of the oxygenreductionreaction (ORR) and the increase in the area-specific resistance (ASR) of the electrodes. A possible solution to the problem of the increase in polarization resistance is through the application of materials that are capable of extending the ORR from the triple-phase boundaries at the cathode/electrolyte interface to the electrode volume, namely, oxides with mixed oxygen-ionelectron conductivity (MIECs) [24] and oxides with proton-electron conductivity (PECs) [25,26]. Among the MIECs, complex oxides with the Ruddlesden-Popper (R-P) structure are widely considered to be prospective cathode materials for IT-SOFCs [27], including the first order R-P phases with a general formula of Ln\({}_{2}\)NiO\({}_{4+\delta}\) (Ln = La, Nd, Pr) [28]. It is worth noting that, in the above-mentioned series, Nd\({}_{2}\)NiO\({}_{4+\delta}\) is characterized by having high phase stability [29] and the lowest level of chemical interaction with the Ce\({}_{0.9}\)Gd\({}_{0.1}\)O\({}_{1.95}\)[30] and YSZ [31] electrolytes. The obtained data on the partial substitution of lanthanide cations by Ca\({}^{2+}\) cations in the Ln\({}_{2}\)NiO\({}_{4+\delta}\) (Ln = La, Nd) series showed a general trend for the total conductivity to increase [31,32]. Nevertheless, oxygen overstoichiometry, oxygen surface exchange and diffusion kinetics, and the electrochemical performance of the La\({}_{2-x}\)Ca\({}_{x}\)NiO\({}_{4+\delta}\)[32, 33, 34] and Nd\({}_{2-x}\)Ca\({}_{x}\)NiO\({}_{4+\delta}\)[32, 35, 36, 37, 31] electrodes were suppressed with Ca-substitution. However, in the case of the Nd-containing electrodes, the suppression was less pronounced than that for the La-containing electrodes. For instance, according to data reported in [33], the polarization resistance values for the La\({}_{2}\)NiO\({}_{4.17}\) and La\({}_{1.7}\)Ca\({}_{0.3}\)NiO\({}_{4.06}\) electrodes on the Ce\({}_{0.8}\)Sm\({}_{0.2}\)O\({}_{1.9}\) electrolyte substrates were equal to 0.73 and 4.01 \(\Omega\) cm\({}^{2}\) at 700 \({}^{\circ}\)C, correspondingly.