Effect of nickel nano-particle sintering on methane reforming activity of Ni-CGO cermet anodes for internal steam reforming SOFCs

摘要

In the present study, a single step synthesis of nano-sized NiO-Ce_(0.9)Gd_(0.1)O2 (NiO-CGO) composite powder was successfully accomplished by a glycine-nitrate-process (GNP) and its catalytic activity for steam reforming of methane (SRM) was investigated in the absence of electrochemical effects. From XRD, SEM and CHN analysis on the spent Ni-CGO cermet catalysts after the test with different flow rates and S/C ratios, we found that the main reason for the decrease in the reforming activity was not due to oxidation or sintering of bulk Ni catalyst and carbon formation on the catalyst surface. Time-on-stream analysis at 800 °C for 80 h showed a continuous decease in the reforming activity for steam rich conditions (S/C =1.5) whereas a constant and moderate reforming activity was observed for steam lean conditions (S/C=0.5). From TEM analysis it is clearly evidenced that the reason for continuous decrease in the reforming activity under steam rich conditions was due to nickel nano-particle sintering whereas no sintering occurred under steam lean conditions which indicated that the steam was primary cause for nickel nano-particle sintering. Furthermore, TEM/EDS analysis confirmed that the nickel nano-partides were mainly located on the surface of the CGO support which can suppress the carbon formation by maintaining good metal (Ni)-support (CGO) interaction even under steam lean conditions.