Thin-film composite electrodes with nanometric grains of platinum and yttria-stabilized zirconia (YSZ) were reactively sputtered onto single-crystal yttria-stabilized zirconia. The activation polarization resistance exhibited an activation energy of 1.3-1.5 eV and was found to have an approximate inverse dependence on microelectrode radius squared, consistent with, effectively, a mixed ionic-electronic conductive nature. Area specific polarization resistances of less than 500 Omega cm(2) were achieved at 400 degrees C in a dense thin-film electrode. The attractiveness of these nanocomposite electrodes for use in microfabricated solid oxide fuel cells (SOFCs), of interest as portable power sources, is discussed. (c) 2007 The Electrochemical Society.