Deactivation of Ceria-Based SOFC Anodes in Methanol

The performance and stability of Cu-ceria-YSZ (yttria-stabilized zirconia) and carbon-ceria-YSZ, solid-oxide-fuel-cell (SOFC) anodes were examined in neat (100%) methanol at 973K and compared to the performance of the same anodes in dry H2. The presence of Cu catalyzed the decomposition of methanol, so that the initial performance of cells with Cu-ceria-YSZ anodes was similar to CO and H2. However, with carbon-ceria-YSZ anodes, the open-circuit voltage was significantly higher and the reaction over-potential significantly lower in methanol than in H2, suggesting that methanol is a more effective reductant of the anode three-phase boundary region. Carbon-ceria-YSZ anodes were found to undergo rapid and irreversible deactivation in methanol. Steady-state rates of methanol decomposition over ceria-YSZ were found to undergo a similar deactivation as the carbon-ceria anodes. Although no evidence for carbon deposition was observed with methanol at 973 K, the addition of steam was found to partially stabilize both anode and catalyst performance. Scanning electron microscopy (SEM) of ceria particles in YSZ showed a large change in the morphology of the ceria particles when the samples were heated in methanol, while negligible changes were observed when heating in H2. It is suggested that the results with methanol can be explained as resulting from the very low P(O2) that is effectively produced by having methanol in contact with ceria.