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)0.95MnO3−δ (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 H2 reached 1.238 at 800 °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 H2 was investigated by gradual loading of the system current. Re-oxidation of Ni, which was not caused by O2 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(H2) 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 O2 before reduced in H2. It is possible that H2O molecules covered on the NiO due to oxidation of Ni by H2O, which hindered NiO to be reduced by H2, could be moved out by O2 burning.