Comparison of the performances of single cell solid oxide fuel cell stacks with Ni/8YSZ and Ni/10CGO anodes with H2S containing fuel

Abstract

The performances of single cell solid oxide fuel cell (SOFC) stacks with Ni/8YSZ (8 mol% Y2O3 doped ZrO2) and Ni/10CGO (10 mol% Gd2O3 doped CeO2) anodes were compared with respect to sulfur poisoning (1–50 ppm) with H2/H2O/N2 fuel mixture at 850 °C. The mechanisms of the sulfur poisoning and regeneration of Ni/8YSZ and Ni/10CGO anodes at the triple phase boundaries are discussed. The effects of various parameters as H2S contamination cycles, H2S concentration, current density, H2O concentration and contamination durations were examined. A mechanism for the progress of the sulfur poisoning in the anode is proposed. It is shown that theoretically it is possible to calculate the nickel surface area accessible for the sulfur adsorption in the anode using H2S poisoning behavior for Ni/8YSZ anodes. The sulfur poisoning mechanisms of Ni/8YSZ and of Ni/10CGO anodes are proposed by taking into account the different oxidation mechanisms of H2 in the anodes considered in previous studies. The higher sulfur resistance of Ni/10CGO is explained with its high mixed ionic electronic conductivity as well as its ability to adsorb H2. Due to these properties CGO can continue electrochemical reactions even when nickel is covered with sulfur.