We demonstrate the high-performance and robust operation of anode-supported solid oxide fuel cells under a mixed-gas atmosphere applying a novel cell structure and characterization method, useful for minimizing the conventional problems of mixed-gas operation with anode-supported solid oxide fuel cells. To achieve the exothermic methane (CH4) partial oxidation and sufficient difference in oxygen partial pressure even in mixed-gas mode, a composite of metallic rhodium and cerium dioxide (CeO2) was chosen as the optimized reforming and oxygen barrier layer after the comprehensive catalytic experiment. We also obtained increased cell operation reliability through the combination of anode pre-reduction, an optimized material system, and a customized characterization jig (including cathode-ahead layout and impinging jet flow). According to the cell test at 600 degrees C under a feeding gas of CH4 and O-2, an open-circuit voltage and maximum power density of 0.916V and 0.422W/cm(2), respectively, were successfully achieved. Copyright (c) 2015 John Wiley & Sons, Ltd.