Trends in catalytic activity for SOFC anode materials

Quantum mechanical calculations on the level of density-functional theory are used to calculate the stability of surface-adsorbed hydrogen atoms, oxygen atoms, and hydroxyl radicals for a variety of metals (Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Pt, Au) that may be used as electrode materials for solid oxide fuel cell (SOFC) anodes. The reaction energies along the hydrogen oxidation pathway were quantified for both, oxygen spillover and hydrogen spillover mechanisms at the three-phase boundary. The ab initio results are compared to previously-obtained experimental anode activities measured for nine different metal/stabilized zirconia anodes. The experimentally-observed variation of electrode activity with anode material is well-correlated with the calculated stability of surface-adsorbed atomic oxygen, but uncorrelated with the stability of surface-adsorbed hydrogen. This finding indicates that oxygen spillover, where adsorbed oxygen is a key intermediate, is the dominant reaction pathway under the conditions used in the experiments. In this way the activity is linked directly to the microscopic binding affinities of reaction intermediates, providing a new understanding of the anode reaction. (c) 2007 Elsevier B.V. All rights reserved.