Survey on electrochemical properties of La2−xSrxNiO4±δ (x = 0.2 and 0.8, δ > 0) cathodes related with structural stability under cathodic polarization conditions

In view of utilization as cathodes for intermediate temperature solid oxide fuel cells (SOFCs), the La2−xSrxNiO4±δ (x = 0.2 and 0.8, δ > 0) series of compounds were evaluated with respect to their electrical conducting, thermomechanical and electrochemical properties. On the one hand, La1.2Sr0.8NiO4−δ exhibits a higher electrical conductivity (>180 S cm−1 in the temperature range 600-800 °C) and a lower electrode polarization under open-circuit voltage conditions (∼0.12 Ω cm2 at 800 °C) than La1.8Sr0.2NiO4+δ, together with a suitable thermal expansion coefficient (13.8 × 10−6 K−1 averaged between 50 and 1000 °C). On the other hand, the structure and electrochemical properties of La1.2Sr0.8NiO4−δ electrode were obviously changed after being subjected to cathodic polarization. The cathodically polarized La1.2Sr0.8NiO4−δ electrode showed an aggregation of strontium oxide onto the surface, concomitant with a degradation of electrochemical properties. By contrast, the structure and electrochemical properties of La1.8Sr0.2NiO4+δ electrode before and after cathodic polarization were basically unvaried. The disparate changes in structure and electrochemical properties of the two electrodes were interpreted in terms of their differing peculiarities in oxygen nonstoichiometry. The results of this work highlight the importance of strontium content and thereby oxygen nonstoichiometry of La1−xSrxNiO4±δ electrodes to their structural stability under cathodic polarization conditions, which is a critical point to be used as cathodes in SOFCs.