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

The cathodic performance of selected mixed-conducting electrodes, including perovskite-type SrMn_0.6Nb_0.4O_3 ? δ, Sr_0.7Ce_0.3Mn_0.9Cr_0.1O_3 ? δ and Gd_0.6Ca_0.4Mn_0.9Ni_0.1O_3 ? δ, and Ruddlesden–Popper La₂Ni_0.5Cu_0.5O_4 + δ, LaSr₂Mn_1.6Ni_0.4O_7 ? δ, La₄Ni_3 ? xCu_xO_10 ? δ (x = 0–0.1) and La_3.95Sr_0.05Ni₂CoO_10 ? δ, was evaluated in contact with apatite-type La₁₀Si₅AlO_26.5 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 La₄Ni_2.9Cu_0.1O_10 ? δ > La₄Ni₃O_10 ? δ > La_3.95Sr_0.05Ni₂CoO_10 ? δ and decreasing on copper doping in K₂NiF₄-type La₂Ni_1 ? xCu_xO_4 ? 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 La₁₀Si₅AlO_26.5, 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.