Sulfur tolerance and hydrocarbon stability of La0.75Sr0.25Cr0.5Mn0.5O3/Gd0.2Ce0.8O1.9 composite anode under anodic polarization

A La0.75Sr0.25Cr0.5Mn0.5O3/Gd0.2Ce0.8O1.9 (LSCM/GDC) composite electrode was developed and applied as a solid oxide fuel cell (SOFC) anode for the direct oxidation of sulfur-containing methane. The anode was fully activated in wet CH4 at 850 degrees C and a constant potential of -0.5 V with respect to a Pt/air reference before the fuel was shifted to wet 0.5% H2S+99.5% CH4. In the sulfur-containing methane fuel, the anodic current dropped from 0.233 A cm(-2) to 0.2 A cm(-2) in a 10 h period, showing a performance degradation rate of ca. 1.4%/hr possibly due to sulfur poisoning. In the subsequent 110 h period, the anodic current tended to be relatively stable with a very small degradation rate of 0.017%/h, which is most likely attributed to the coarsening of the electrode microstructure. Though some impurities, such as MnS, La2O2S, and alpha-MnOS, were detected in the X-ray diffraction analysis of the anode after 120 h of stability test, the scanning electron microscopy micrographs and energy-dispersive X-ray analysis showed that no carbon and sulfur deposition was found on the cross-sectional surface of the anode. The results suggest that the LSCM/GDC composite is a promising candidate material for an anode and has much better hydrocarbon stability and sulfur tolerance under the anodic polarization than Ni-based cermets.