Strategies for Tuning the Electrical Properties of La ₂ NiTiO ₆ Perovskite Derivatives and Their Evaluation as Potential Air Electrodes in Reversible Solid Oxide Cells

The perovskite-like materials La1.60Ce0.10Sr0.30NiTiO6-δ (LCSNT102000) and La1.60Ce0.10Sr0.20NiTiO6-δ (LCSNT101010) are obtained by cosubstituting La3+ with Ce4+ and Sr2+ in La2NiTiO6-δ and in the A-site-deficient derivative La1.90NiTiO6-δ, respectively. In both perovskites, conductivity is due to small polarons hopping. In LCSNT101010, which displays lower conductivity and higher activation energy than LCSNT102000, this mechanism is hindered due to fewer Ni–O–Ni conduction paths (because Ni/Ti antisite defects are scarce) and to some kind of defect association, which acts as a charge-carriers trap. The presence of Ce4+ in LCSNT102000 and LCSNT101010 provides a suitable redox pair, Ce4+/Ce3+, for n-type conduction under reducing conditions, with the activation of the Ti4+/Ti3+ pair ruled out based on the XAS data. The low concentration of Ce4+ limits the n-type conduction to highly reducing atmospheres (pO2 < 10–18 atm) and low conductivity values. This, together with the chemical incompatibility of both materials with YSZ and CGO under reducing conditions, suggests that they can be used as components of the air electrode in reversible SOCs. LCSNT101010 displays performance as a cathode in SOFC comparable to LCSNT102000; however, its behavior as an SOEC anode is much worse, mainly due to its very poor ionic conductivity (estimated oxide diffusion coefficients at 900 °C are 4.9 × 10–11 and 1.7 × 10–9 cm2 s–1, respectively). Finally, LCSNT102000 presents similarly low ASR values under anodic and cathodic polarization, which are lower than those corresponding to the OCV. This material could potentially be used as an air electrode in a reversible cell.