Spatially Heterogeneous Chemistry Observed using NIRTI on SOFC Anodes

Abstract

Carbon formation remains the primary degradation mechanism for solid oxide fuel cells (SOFCs) operating on carbonaceous fuels. The mechanisms for the remediation of carbon (C) induced degradation via electrochemical gasification and reforming using O2(g) and H2O(g) was studied using Near Infrared Thermal Imaging (NIRTI), Fourier Transform Infrared Emission Spectroscopy (FTIRES), chronoamperometry/chronopotentiometry (CA/CP), and mass spectrometry (MS). Carbon removal follows a stepwise mechanism, first oxidizing surface carbon to CO(g), and subsequently to CO2(g). CO(g) oxidation requires a catalytic surface to form CO2 which plays a key role in removing C via the reverse Boudouard chemistry. NIRTI reveals spatially heterogenous chemistry and suggests a specific role of surface oxygen species. These species form from dissociative adsorption and non-faradaic oxide flux through the electrolyte, as well as O2 transport limited processes occurring due to high O2 utilization. C removal from electrochemical oxidation and steam spatially homogeneous compared to O2, due in part to the respective active surface species, and their respective transport limitations. Under O2 C removal is appears incomplete, despite electrochemical results. These experiments clarify the mechanisms responsible for remediation of C on SOFC anodes and highlight the need of spatially resolved techniques to study SOFCs under operating conditions.