A new technique for the fabrication of dense yttria-stabilized zirconia (YSZ) thin-film electrolytes (between 3 and 10 mum) on porous electrode substrates has been used to make planar solid-oxide fuel cells (SOFCs). The YSZ electrolyte is strongly bonded to the Ni-YSZ and La0.89Sr0.1MnO3 (LSM)-YSZ electrode substrates, and the power density of a Ni-YSZ/YSZ/LSM-YSZ cell is over 0.8 W/cm(2) at 800 degreesC. Initial investigations of doped YSZ mixed-conducting electrodes in our thin-film YSZ cells indicate that Tb- and Ti-doped YSZs enhance cell power densities from 15 to 50% at 800 degreesC. New Cu-CeO2-YSZ anodes for the dry oxidation of methane have also been investigated. Initial results show that the Cu-CeO2-based anodes are stable in hydrocarbon fuels, and that the principle anodic reaction is a direct, electrocatalytic oxidation of the hydrocarbon fuel.