Rapid degradation mechanism of Ni-CGO anode in low concentrations of H2 at a high current density

Cathode-supported solid oxide fuel cell (SOFC) consisting of a Ni-Gd0.2Ce0.8O1.9 (Ni-CGO) anode with a Sc2O3-doped ZrO2 (ScSZ) electrolyte on a (La0.75Sr0.25)(0.95)MnO3-delta (LSM)+CGO cathode substrate was fabricated via a dual drying pressing followed by co-firing method. Open circuit voltage (OCV) of as-prepared cell in pure H-2 reached 1.238 at 800 degrees C, indicating that the ScSZ electrolyte film prepared by the present method was dense enough and the cell was in a well-sealed state. Performance degradation phenomenon of Ni-CGO anode in low concentration of H-2 was investigated by gradual loading of the system current. Re-oxidation of Ni, which was not caused by O-2 in the case of mechanical damage, was supposed to occur at a high current density. According to the EIS and SEM analysis results, it is inferred that the Ni could be oxidized by the oxygen ion at a high current density in low concentration of H2 as well as by the produced H2O with a high p(H2O)/p(H-2) ratio. In this case, the performance of the degraded cell was unable to be directly regenerated by hydrogen reduction unless the anode was firstly burnt in O-2 before reduced in H-2. It is possible that H2O molecules covered on the NiO due to oxidation of Ni by H2O, which hindered NiO to be reduced by H-2, could be moved out by O-2 burning. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.