Abstract
Iridium-carbon composite films were prepared by metalloorganic chemical vapor deposition (MOCVD) on yttria stabilized zirconia (YSZ) substrates using an iridium acetylacetonate precursor. The films prepared without oxygen gas addition were black-colored and contained 35 to 70vol% carbon. The carbon was amorphous surrounding iridium grains of 1 to 3 nm in diameter. The Ir-C films showed excellent electrical and catalytic properties for YSZ as a reversible electrode at less than 800K. The impedance associated with the YSZ/Ir-C interface was about 1/3 to 1/5 smaller than that of sputtered Pt electrodes at 773K. By adding a small amount of oxygen gas in the source gases, the carbon content in the films decreased significantly accompanying grain growth of Ir and degradation of electrical performance. The output current using the Ir films containing a trace of carbon (about lmass%C) as electrodes was still four times greater than that using the Pt electrodes at 773K.
