The electrochemical behaviour of Ni-Ce0.9Gd0.1O2-delta (Ni-CGO) with a NiO content of 2.5 and 70 wt.% was investigated by impedance spectroscopy. Symmetrical cells with yttrium-stabilized zirconia as electrolyte were prepared with screen printing and then sintered at 1250 degreesC for 5 h. The microstructure of the anode material after sintering was analysed by SEM. Impedance spectroscopy measurements were carried out in atmospheres containing H-2, CH4 and N-2, at various compositions humidified with 3% H2O in the temperature range 700-850 degreesC. No visible carbon deposition on both electrodes was found after measurements in variable atmospheres of H-2 and CH4 (Balance N-2) despite the high content of Ni. However, carbon deposition occurred on the anode with 70 wt.% NiO during continuous exposure in stability testing for 90 h in 97% CH4/3% H2O.