A first-principles analysis of electrocatalytic oxidation of Co at the Dmfc anode

A key factor limiting the anode performance in the direct methanol fuel cell is the poisoning of Pt by CO, an abundant surface intermediate that forms in methanol oxidation. The energetics of CO oxidation over Pt and different Pt-Ru alloys were studied. The influences of solution and electrochemical potential on the overall reaction energies and activation barriers were examined. The addition of ruthenium to a Pt surface significantly reduced the equilibrium potential of water activation, thus indicating that the bifunctional mechanism contributes substantially to the oxidation of CO. The introduction of Ru into Pt, however, also acted to increase the equilibrium potential for the overall reaction of CO and H₂O to form CO₂, two protons and two electrons. The equilibrium overpotential for the overall oxidation of CO with H₂O was substantially reduced in the overlayer system due to decreased binding energies of both species. A combined alloy system, with a mixed Pt/Ru layer over a Ru bulk substrate was shown to combine both the bifunctional and ligand effects. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).