Low carbon emissions are perceived as the main target and direction in the global development. It is therefore of importance to explore new energy conversion technologies, to efficiently take advantage of the available green energy resources. Solid Oxide Cells (SOCs) are considered as one of the most promising options, since depending on the demand, they can provide both hydrogen and electricity generation in the same device. In SOCs, the main decisive factor for the efficiency is performance of the oxygen electrode, of which cobalt-containing perovskite-type materials are usually utilized due to their extraordinary electrocatalytic properties at lowered operation temperatures (500-800 °C) [1]. Meanwhile, given that the new concept of the high entropy oxides is proved to be very successful in materials science, it is of great interest to develop and study novel, multicomponent perovskites as candidate oxygen electrode materials. In fact, initial data showed promising performance, with a possibility to limit Co content [2]. Apart from the chemical content optimization, morphology of the oxygen electrode can be also enhanced, which is undoubtedly crucial to influence the oxygen reduction/evolution reaction mechanism. This can be potentially realized by the electrospinning technique, bringing new possibilities for improving the oxygen electrodes.
Taking all those concerns mentioned above into account, in this work, perovskite-type materials with varied substitution, La_0.6Sr_0.4Ni_0.15Mn_0.15Fe_0.15Cu_yCo_0.55-yO_3-δ (y = 0.05-0.20) were synthesized and characterized systematically. X-ray diffraction results confirmed that all compounds are well-crystallized, without any impurities observed, and exhibit rhombohedral symmetry (R-3c). Their structures are stable at high temperatures, up to 900 °C. Only slight variations of the oxygen content with temperature were measured, suggesting mild thermal expansion behavior. High total electrical conductivity was observed for all compounds, above 200 S cm^-1, and interestingly, a negative Seebeck coefficient was detected, suggesting that the main charge carriers are electrons (polarons). The electrochemical characterization in symmetrical cells (based on GDC solid electrolyte) showed an increased catalytic activity with the increasing Co content. However, even the relatively low Co content La_0.6Sr_0.4Ni_0.15Mn_0.15Fe_0.15Cu_0.20Co_0.35O_3-δ electrode demonstrated a desired, low polarization resistance value of only 0.018 Ω cm² at 850 °C. This could be further enhanced by over 20%, if the material was obtained by the electrospinning. The excellent performance was also proved in the full cell measurements, in which a peak power density over 1.0 W cm^-2 was reached at 850 °C, as well as a promising performance was measured in the electrolysis mode.