First principle density functional theoretical calculations carried out within a constant potential half-cell formalism were used to model the electro-oxidation of CO over Pt(1 1 1). The method involves tuning the potential by the addition or removal of electrons from the system. The free energy for different adsorbed species within the double-layer is analyzed over a range of different potentials to establish the lowest energy states and the reaction energies that connect these states. The potentials are calculated based on a novel double-reference approach [J.S. Filhol, M. Neurock, Angew. Chem. Int. Ed. 45 (2006) 402] discussed earlier. The potential-dependent reaction energies are reported for the elementary steps of water activation in the presence of co-adsorbed CO and CO oxidation over the model Pt(1 1 1) surface. The potential-dependent activation barriers are computed for the key elementary steps in CO oxidation to develop a detailed reaction energy profile as a function of electrode potential. The results suggest that the coupling of co-adsorbed CO and OH controls the rate. Water activation, however, is necessary to supply a critical coverage of the surface OH oxidant.
Bibliographical noteFunding Information:
This work is supported by the Army Research Office—MURI grant (DAAD19-03-1-0169) for fuel cell research. Computational resources at the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory were used, in part, to complete this research as well as computing resources at the U.S. Army Research Laboratory Major Shared Resource Center. The authors thank Dr. Sally Wasileski and Dr. Chris Taylor for helpful discussions.
- CO electro-oxidation
- Density functional theory
- Direct methanol fuel cells
- Pt(1 1 1)