Sulfur Poisoning of SOFCs: Voltage Oscillation and Ni Oxidation

Abstract

Sulfur is one of the major contaminants for SOFC anodes, and can cause performance degradation of SOFC systems. In the present study, H2S poisoning phenomena are analyzed at around 800°C, using electrolyte-supported single cells to understand Ni anode degradation mechanisms, especially under relatively oxidizing conditions. Anode performance degradation caused by sulfur in partially or fully pre-reformed CH4–based fuels has been evaluated as a function of various operational parameters, including; operational temperature, pre-reforming ratio, steam-to-carbon ratio, fuel utilization, and current density, for different fuel compositions. Besides the well-known change in cell voltage by the reversible surface adsorption/desorption mechanism, sulfur poisoning phenomena associated with voltage oscillation and Ni oxidation are newly found at high fuel utilizations and at high current densities, respectively. Such degradation is associated with the increase in the O/Ni ratio, and grain growth of Ni-based particles in the anodes.