The Oxidation of H2 and CH4 on an Oxygen-Enriched Yttria-Stabilized Zirconia Surface: A Theoretical Study Based on Density Functional Theory

The mechanism of fuel (molecular hydrogen and methane) adsorption and oxidation on an yttria-stabilized zirconia (YSZ) surface, used as part of the anode in solid oxide fuel cells (SOFC), is investigated employing ab initio periodic calculations based on density functional theory. Our results indicate that exothermic adsorption and decomposition of the fuel is possible if the vacant sites of YSZ are filled by externally supplied oxygen atoms from the SOFC cathode or other sources. In agreement with experimental observations, we find that formaldehyde is an intermediate gas phase species, whereas formate is a stable intermediate surface species in the process of methane decomposition and oxidation on YSZ. These findings underline that direct oxidation of fuel on the electrolyte surface is possible without the need for a metallic catalyst if the vacant sites on YSZ can be filled by oxygen atoms from the SOFC cathode at a sufficiently high rate. Our results are in line with recent experimental findings in which CH4 and H-2 were oxidized by an oxygen-enriched YSZ surface.