Properties of pyrochlore ruthenate cathodes for intermediate temperature solid oxide fuel cells

Abstract

Powders of Bi2Ru2O7.3, Pb2Ru2O6.5, and Y2Ru2O7 were prepared and their reactivity with Ce0.9Gd0.1O1.95 (CGO) electrolyte powders examined. Bi2Ru2O7.3 and Pb2Ru2O6.5 reacted with CGO but Y2Ru2O7 appeared stable when heated in contact with CGO powder at 900C for 24 h. Symmetrical electrodes of Y2Ru2O7-x were deposited on CGO ceramic pellets, either by tape-casting or by electrostatic assisted chemical vapor deposition (EACVD) techniques, and cathode resistivities determined by impedance spectroscopy. Undoped Y2Ru2O7 electrodes exhibited very high area specific resistivities (ASR) at 627C (similar to 4000 Ohm cm(2)), but by doping with SrO the resistivity was reduced almost 100 x to 47 Ohm cm(2). The behavior of the Y2Ru2O7 cathodes was interpreted in terms of available oxygen ion transport data for the Gd2Ti2O7 series, and it was concluded that optimization of pyrochlore ruthenate compositions should be possible to improve further the oxygen reduction behavior of ruthenate cathodes for intermediate temperature solid oxide fuel cells.