The electrochemical properties of a composite (NiO)x-(yttria-stabilized zirconia (YSZ))(1-x) working electrode for a new type of electrochemical cell for NO decomposition in the presence of excess oxygen are investigated. It is shown that the dependence of the NO conversion on the value of the current passed through the electrochemical cell with a nanoporous (NiO)(x)-(YSZ)(1-x) working electrode is linear and that the value of current efficiency depends on the NO and 0, gas concentrations only (eta = [NO]/([NO] + 2[O-2]). The optimum NiO addition (35% by volume) to the YSZ resulted in a decrease of the cell operating voltage and, as a result, in a decrease in the electrical power required for NO decomposition. The observed high performance of the composite working electrode at this composition is consistent with the effective medium percolation theory, which predicts the ambipolar transport behavior of the composite mixed ionic-electronic (YSZ-NiO) conductors as a function of the volume fraction of each of the randomly distributed constituent phases.