Kinetics of methane electrooxidation in pure and composite anodes of La0.3Y0.1Sr0.4TiO3-delta

Abstract

The electrochemical characteristics of electrolyte-supported solid oxide fuel cells containing pure perovskite anode of La0.3Y0.1Sr0.4TiO3-(delta), (LYSTA-) and composite anodes with varying fractions (30 and 50 wt%) of yttria-stabilized zirconia (YSZ), LYSTA- (30)YSZ and LYSTA- (50)YSZ, were studied in humidified methane. The 8 wt% CeO2 and 4 wt% NiO, denoted as (84), were impregnated into the pure and composite anodes for efficient electrooxidation of methane. The studies were carried out to qualitatively estimate the kinetic parameter, exchange current density (i(o)), for methane electrooxidation. Evaluation in a 3-electrode configuration with an asymmetric reference electrode yielded the following activity trend: (84)LYSTA- > (84)LYSTA- (30)YSZ > (84)LYSTA- (50)YSZ in the high-overpotential region, with i(o) values of 133.2 +/- 32.5, 40.8 +/- 16.6, and 47.9 +/- 16.3 mA cm(-2) at 900 degrees C, respectively. The presence of YSZ in the composite anodes leads to decrease in i(o) and degrading performance. Impedance studies clubbed with equivalent circuit modeling along with physical characterization were used to account for decreased i(o) values in composite anodes. Metal support interactions arising between Ni and CeO2 are studied using a high-resolution transmission electron microscope. Solid oxide fuel cell (SOFC) studies with (84)LYSTA- anode yielded a maximum power density of 591 mW cm(-2) in hydrogen and 429 mW cm(-2) in methane.