Trends for Methane Oxidation at Solid Oxide Fuel Cell Conditions

Abstract

First-principles calculations are used to predict a plausible reaction pathway for the methane oxidation reaction. In turn, this pathway is used to obtain trends in methane oxidation activity at solid oxide fuel cell (SOFC) anode materials. Reaction energetics and barriers for the elementary reaction steps on both the close-packed Ni{111} and stepped Ni{211} surfaces are presented. Quantum-mechanical calculations augmented with thermodynamic corrections allow appropriate treatment of the elevated temperatures in SOFCs. Linear scaling relationships are used to extrapolate the results from the Ni surfaces to other metals of interest. This allows the reactivity over the different metals to be understood in terms of two reactivity descriptors, namely, the carbon and oxygen adsorption energies. By combining a simple free-energy analysis with microkinetic modeling, activity landscapes of anode materials can be obtained in terms of these two descriptors. This not only simplifies the view of the oxidation process but it also gives insight into which reaction pathways are likely to be dominant over the different transition-metal anode materials. Most importantly, it reveals the properties the ideal alloy catalyst should possess.