Reactions of low and middle concentration dry methane over Ni/YSZ anode of solid oxide fuel cell

Abstract

Directly using methane in solid oxide fuel cells (SOFC) requires the knowledge of the reaction of methane over the anode. The reactions of low and middle concentration dry methane were studied over the anode of solid oxide fuel cell with Ni/yttria-stabilized zirconia (YSZ) anode and YSZ electrolyte. The production rates of different types of gas at anode outlet were measured at different current density. Mass balance and relationships between production rates and reaction rates were used to analyze the chemical and electrochemical reactions that took place in parallel. When dry methane is in low concentration, methane decomposition and deposited carbon oxidation occurs at low current density with the overall reaction being partial oxidation of methane (POM). With increased current density, hydrogen oxidation and carbon monoxide oxidizing to carbon dioxide take place simultaneously, and the overall reaction becomes the direct oxidation of methane (DOM). When DOM occurs, a portion of methane participates the POM. However, the rate of POM decreases with increased current density. At medium methane concentration, only partial oxidation of methane takes place. Carbon deposition was found in all the tests across the concentration range investigated.