Effects of the Sm0.2Ce0.8O2-delta Modification of a Ni-Based Anode on the H2S Tolerance for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

The H2S tolerance and stability of a Sm0.2Ce0.8O2-delta 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 degrees C and 700 degrees 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 H2S, 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 Ce2O2S 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. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.071302jes] All rights reserved.