Sulfur Tolerance and Hydrocarbon Stability of La[sub 0.75]Sr[sub 0.25]Cr[sub 0.5]Mn[sub 0.5]O[sub 3]∕Gd[sub 0.2]Ce[sub 0.8]O[sub 1.9] Composite Anode under Anodic Polarization

Abstract

A La0.75 Sr0.25 Cr0.5 Mn0.5 O3 Gd0.2 Ce0.8 O1.9 (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°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% H2 S+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, La2 O2 S, and α-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. © 2007 The Electrochemical Society.