Evaluation of apatite silicates as solid oxide fuel cell electrolytes

Apatite-type silicates have been considered as promising electrolytes for Solid Oxide Fuel Cells (SOFC); however studies on the potential use of these materials in SOFC devices have received relatively little attention. The lanthanum silicate with composition La10Si5.5Al0.5O26.75 has been evaluated as electrolyte with the electrode materials commonly used in SOFC, i.e. manganite, ferrite and cobaltite as cathode materials and NiO-CGO composite, chromium-manganite and Sr2MgMoO6 as anode materials. Chemical compatibility, area-specific resistance and fuel cell studies have been performed. X-ray powder diffraction (XRPD) analysis did not reveal any trace of reaction products between the apatite electrolyte and most of the aforementioned electrode materials. However, the area-specific polarisation resistance (ASR) of these electrodes in contact with apatite electrolyte increased significantly with the sintering temperature, indicating reactivity at the electrolyte/electrode interface. On the other hand, the ASR values are significantly improved using a ceria buffer layer between the electrolyte and electrode materials to prevent reactivity. Maximum power densities of 195 and 65 mWcm−2 were obtained at 850 and 700 °C, respectively in H2 fuel, using an 1 mm-thick electrolyte, a NiO-Ce0.8Gd0.2O1.9 composite as anode and La0.6Sr0.4Co0.8Fe0.2O3−δ as cathode materials. This fuel cell was tested for 100 h in 5%H2–Ar atmosphere showing stable performance.