Effects of the Sm_0.2Ce_0.8O_2-δ modification of a ni-based anode on the H₂S tolerance for intermediate temperature solid oxide fuel cells

The H₂S tolerance and stability of a Sm_0.2Ce _0.8O_2-δ coating on the Ni/YSZ anode pore wall surface was investigated. The sulfur poisoning mechanisms were studied for various H₂S concentrations (0-100 ppm) and temperatures (600°C and 700°C) under both open circuit voltage (OCV) and current-loading conditions. For the unmodified Ni/YSZ anode under current-loading conditions, the cell performance decreased significantly with the introduction of H ₂S, as the sulfur strongly adsorbed at the electrochemical reaction sites (ERSs). For the SDC-modified Ni/YSZ anode under the OCV conditions, the governing mechanism of the H₂S poisoning was the formation of Ce ₂O₂S with low oxygen ion conductivities, making the oxygen ion path disconnected. For the SDC-modified anode under current-loading conditions, the mixed ionic and electronic conductivity (MIEC) of the SDC allowed the electrochemical reactions to occur mainly at the SDC/fuel interface (2PB). With these conditions, the adsorbed sulfur was easily removed by the electrochemical oxidation. The decrease in the sulfur poisoning effect resulted in stable cell performances at 500 ppm of H₂S over 800 h.