Critical S/C Ratio of the Carbon Deposition in the SOFC Anode Using CH4: In-Situ Analysis of the Anode Surface

Abstract

Surface species on the anode of SOFC using methane was measured by an in-situ infrared (IR) spectroscopy with synchrotron radiation during discharge (S/C (steam-to-carbon) = 0.03) and non-discharge (S/C = 0) modes at SPring-8. The carbon deposition was found in IR spectra during 30 min exposure in CH4 environment in non-discharge mode (S/C = 0). However, the carbon deposition was not found in IR spectra in discharge mode (S/C = 0.03). During measurement, an excess CH4/H2O gas was introduced into the chamber; therefore, H2O remained on the Ni/YSZ surface even at S/C = 0.03, resulting in preventing the carbon deposition through steam reforming reaction. Calculation showed that the carbon deposition occurred when the carbon deposition rate exceeded the reforming rate. It was suggested that a critical S/C ratio, at which the carbon deposition started to occur, was determined from the balance between the carbon deposition and reforming rates.