Performance of perovskite-related oxide cathodes in contact with lanthanum silicate electrolyte

The cathodic performance of selected mixed-conducting electrodes, including perovskite-type SrMn0.6Nb0.4O3 − δ, Sr0.7Ce0.3Mn0.9Cr0.1O3 − δ and Gd0.6Ca0.4Mn0.9Ni0.1O3 − δ, and Ruddlesden–Popper La2Ni0.5Cu0.5O4 + δ, LaSr2Mn1.6Ni0.4O7 − δ, La4Ni3 − xCuxO10 − δ (x = 0–0.1) and La3.95Sr0.05Ni2CoO10 − δ, was evaluated in contact with apatite-type La10Si5AlO26.5 solid electrolyte at 873–1073 K and atmospheric oxygen pressure. The electrochemical activity of porous nickelate-based layers was found to correlate with the concentration of mobile ionic charge carriers and bulk oxygen transport, thus lowering in the series La4Ni2.9Cu0.1O10 − δ > La4Ni3O10 − δ > La3.95Sr0.05Ni2CoO10 − δ and decreasing on copper doping in K2NiF4-type La2Ni1 − xCuxO4 − δ. The relatively high overpotentials of nickelate-based cathodes, varying in the range − 240 to − 370 mV at 1073 K and current density of − 200 mA/cm2, are primarily associated with surface diffusion of silica from La10Si5AlO26.5, which partially blocks the electrochemical reaction zone. As compared to the intergrowth nickelate materials, the manganite-based electrodes exhibit substantially worse electrochemical properties, in correlation with the level of oxygen-ionic and electronic conduction in Mn-containing phases. The effects of cation interdiffusion between the cell components as a performance-deteriorating factor are briefly discussed.