Porous cell stacks with composite electrodes of La0.85Sr0.15CoxMn1-xO3-Ce0.9Gd0.1O1.95 were tested for activity toward selective electrochemical reduction of NOx to N-2 in the presence of 10% O-2. The cell stacks were produced by tape casting, laminating and sintering the backbone structure followed by infiltration with BaO or La0.85Sr0.15MnO3+delta. The cell stacks were tested in an atmosphere of 1000 ppm NO or NO2 + 10% O-2 in Ar with 10% O-2 in Ar as reference, and in the temperature range of 250 to 500 degrees C. The cell stacks were investigated electrochemically with cyclic voltammetry and polarization, and the outlet gas composition was monitored. Doping with Co increases the electrodes activity for reducing NOx, and up to 93% conversion in the presence of 10% O-2 at 400 degrees C was measured. Infiltration with BaO was necessary to achieve any formation of N-2. Square wave polarization increased the activity of the electrodes achieving a current efficiency as high as 20% at 350 degrees C, and this indicates a problem with mass transfer. An atmosphere containing NO2 also increased the activity of the electrodes, which points to a mechanism with a NO2 related intermediate. (C) 2014 The Electrochemical Society. All rights reserved.