Vibrational Raman spectroscopy, IR emission spectroscopy and near IR thermal imaging coupled with voltammetry and impedance measurements was used to explore the effects of chlorine on electrolyte supported solid oxide fuel cell (SOFC) performance and durability.  Ni-YSZ SOFC anodes were exposed to 110 ppm dry CH₃Cl at 650°C and 700˚C for up to four hours while intermittently exposing the cell to either methane (CH₄) or a biogas surrogate (methane/carbon dioxide; 50:50 by mole fraction) for ten minute intervals. In these experiments Raman spectroscopy was used to monitor carbon accumulation kinetics. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements performed with cells at 650˚C operating with CH₄ (and exposed to CH­₃Cl) showed marked degradation.  Degradation with biogas was even more aggressive.  In both instances, degradation was irreversible as removal of the chlorine source did not result in complete recovery of performance.  These findings stand in contrast to previously reported results of SOFCs operating with H₂ in the presence of a chlorine contaminant.  Curiously, at 700˚C degradation slows significantly with cell performance diminishing slightly before reaching an asymptotic limit.  These results suggest that the presence of carbon facilitates formation of volatile nickel chloride species resulting in substantive damage to anode microstructure.