Carbon formation or "coking" on solid oxide fuel cell (SOFC) anodes adversely affects performance by blocking catalytic sites and reducing electrochemical activity. Quantifying these effects, however, often requires correlating changes in SOFC electrochemical efficiency measured during operation with results from ex situ measurements performed after the SOFC has been cooled and disassembled. Experiments presented in this work couple vibrational Raman spectroscopy with chronopotentiometry to observe directly the relationship between graphite deposited on nickel cermet anodes and the electrochemical performance of SOFCs operating at 725 °C. Raman spectra from Ni cermet anodes at open circuit voltage exposed to methane show a strong vibrational band at 1556 cm(-1) assigned to the "G" mode of highly ordered graphite. When polarized in the absence of a gas-phase fuel, these carbon-loaded anodes operate stably, oxidizing graphite to form CO and CO(2). Disappearance of graphite intensity measured in the Raman spectra is accompanied by a steep ∼0.8 V rise in the cell potential needed to keep the SOFC operating under constant current conditions. Continued operation leads to spectroscopically observable Ni oxidation and another steep rise in cell potential. Time-dependent spectroscopic and electrochemical measurements pass through correlated equivalence points providing unequivocal, in situ evidence that identifies how SOFC performance depends on the chemical condition of its anode. Chronopotentiometric data are used to quantify the oxide flux necessary to eliminate the carbon initially present on the SOFC anode, and data show that the oxidation mechanisms responsible for graphite removal correlate directly with the electrochemical condition of the anode as evidenced by voltammetry and impedance measurements. Electrochemically oxidizing the Ni anode damages the SOFC significantly and irreversibly. Anodes that have been reconstituted following electrochemical oxidation of carbon and Ni show qualitatively different kinetics of carbon removal, and the electrochemical performance of these systems is characterized by low maximum currents and large polarization resistances.

Experiments performed in this work explored how Ni-YSZ cermet anodes infiltrated with 1% Sn or 1% BaO mitigate carbon formation compared to undoped Ni-YSZ anodes in functioning solid oxide fuel cells (SOFCs). In situ vibrational Raman spectroscopy was used to study the early stages of carbon accumulation on the SOFC anodes at 730 °C with methane and under open circuit voltage (OCV) conditions. Additionally, carbon removal with different gas phase reforming agents was evaluated. The effects of these phenomenacarbon accumulation from methane and carbon removal by reforming agentson the electrochemical capabilities of a device were monitored with electrochemical impedance and voltammetry measurements. Vibrational spectra showed that the undoped and 1% Sn infiltrated anodes were very susceptible to carbon formation from methane while considerably less carbon accumulated on the 1% BaO anodes. Electrochemical data, however, implied that carbon accumulated in different regions of the anode and that both Sn and BaO effectively reduced carbon accumulation but also inhibited electrochemical oxidation. For each anode, H 2 O was the most effective reforming agent for removing carbon followed by O 2 and then CO 2 . H 2 O and CO 2 , however, left the anode only partially oxidized, while prolonged exposure to O 2 completely oxidized Ni to nickel oxide. The spectroscopic and electrochemical data showed strong correlations that provide mechanistic insight into the consequences of adding secondary materials to SOFC anodes with the intent of reducing carbon accumulation.

The front cover artwork is provided by the Eigenbrodt (Villanova University, USA) and Walker (Montana State University, USA) research groups. The cover picture shows a background image of the operando spectroscopy apparatus focusing the Raman laser onto the solid oxide fuel cell's Sr2Fe1.5Mo0.5O6‐δ anode catalyst at 800 °C. The forefront of this cover photo showcases Raman spectra that reveal that the anode catalyst has the ability to resists detrimental graphite deposits during fuel cell operation with direct alcohol fuels. Read the full text of the Article at https://doi.org/10.1002/celc.201800827.

A combination of operando Raman spectroscopy and chronoamperometry was used to examine the carbon tolerance of Sr2Fe1.5Mo0.5O6‐δ (SFMO) electrode catalysts when operating with direct methanol and ethanol fuels in solid oxide fuel cells (SOFCs). Chronoamperometry studies revealed that these devices could maintain a steady power density output under typical SOFC operating conditions. High‐temperature Raman measurements of SFMO coupons exposed to methanol and ethanol (and their gas phase pyrolysis products) showed the presence of spectroscopic features associated with ordered and disordered forms of graphitic carbon. However, once SFMO was employed as an anode in an electrolyte‐supported SOFC, the graphite features disappear implying that these materials are not susceptible to carbon accumulation in functioning devices. These electrochemical and operando Raman measurements provided insight into SFMO's ability to act as an effective anode catalyst for SOFCs operating with direct alcohol fuel sources.

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