Chlorine-Induced Degradation in Solid Oxide Fuel Cells Identified by Operando Optical Methods

Chlorine in the form of HCl or CH3Cl can accelerate degradation of solid oxide fuel cell (SOFC) Ni-based anodes through several proposed mechanisms. However, many of these mechanisms were developed with H2 as the primary SOFC fuel, and the effects of chlorine on SOFC anodes operating with carbon containing fuels have not been studied in detail. Experiments described in this work use a suite of independent, complementary techniques to examine chlorine-induced degradation of a SOFC operating with methane at 700 °C. Operando Raman and FTIR-emission spectroscopy, electrochemical characterization, and near-IR thermal imaging coupled with ex-situ field emission scanning electron microscopy provide interlocking data that illustrate how chlorine inhibits CH4 activation on the anode’s Ni catalyst. Raman spectroscopy is used to monitor carbon formation (a signature of methane cracking), while the SOFC is exposed to 100 ppm chlorine and intermittently exposed to methane for 10 min intervals. Linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) show marked degradation, while both carbon accumulation and P CO2 above the anode decrease. Compared to degradation rates in SOFCs exposed to chlorine and operating with hydrogen, degradation with methane is greatly accelerated. Additional differences between SOFCs operating with hydrogen and methane are observed in their ability to recover performance after chlorine is removed from the incident fuel.