The role of metal (Au, Pt, and Ag) electrodes in yttria-stabilized zirconia (YSZ) electrolyte-based impedancemetric nitric oxide (NO) sensors is investigated using impedance spectroscopy and equivalent circuit analysis. Focus on the metal/porous YSZ interface is based on previous studies using a symmetric cell (metal/YSZ(porous)/YSZ(dense)/YSZ(porous)/metal) and attempts to further elucidate the important processes responsible for sensing. The current test cell consists of a rectangular slab of porous YSZ with two metal-wire loop electrodes (metal/YSZ(porous)/metal), both exposed to the same atmosphere. Of the electrode materials, only Au was sensitive to changes in NO concentration. The impedance behavior of porous Au electrodes in a slightly different configuration was compared with dense Au electrodes and was also insensitive to NO. Although the exact mechanism is not determined, the composition and microstructure of the metal electrode seem to alter the rate-limiting step of the interfering O-2 reaction. Impedance behavior of the O-2 reaction that is limited by processes occurring away from the triple-phase boundary may be crucial for impedancemetric NO sensing. (c) 2007 The Electrochemical Society.