Influence of Dry Methane Reactions on the Cell Output Characteristics of Solid Oxide Fuel Cells

Abstract

In order to study the influence of dry methane concentration on outputs in solid oxide fuel cells (SOFCs), the output performance was obtained for dry methane of different concentrations on a Ni-ScSZ anode in solid oxide fuel cells, and the anode exhaust gas was measured by online chromatography. The underlying causes of the output performance change were analyzed from the anode reactions by summarizing the anode exhaust gas regular pattern for different reactions, and analyzing the electrochemical reaction kinetics of methane with oxygen ion. As the oxygen ion concentration at the anode three-phase boundary proportionally increased with current density, the following reactions occurred for different dry methane concentrations in sequence CH 4 + O 2﹣ → CO + 2H 2 + 2e ﹣ , CH 4 + 2O 2 ﹣ → CO + H 2 O + H 2 + 4e ﹣ , CH 4 + 3O 2 ﹣ → CO + 2H 2 O + 6e ﹣ , CH 4 + 4O 2 ﹣ → CO 2 + 2H 2 O + 8e ﹣ . With various concentrations of methane at a low current, the outlet methane continuously reduced with the increase of the current density. Meanwhile, CO and H 2 exhaust gas increased with increasing current density for low concentration of methane. With methane concentrations at 3.85% and 5.66%, the cell output voltage dropped rapidly. For concentrations of 29.7% and 3.85%, the anode exhaust residual methane changed irregularly with current density and this phenomenon was associated with the dry methane that reacted on anode of the cell. The transformation of reactions, the water produced in the electrochemical reactions and the polarization in response to the change of reactions maybe induced the output voltage and power density reducing as low concentrations of dry methane were used.