| The oxygen reduction reaction (ORR) mechanism on Pt(111) was identified using density functional theory (DFT) calculations. The interaction of oxygen with Pt in the presence of the electric double layer was evaluated by treating the electrostatic and solution effects separately. Electrostatic effects modeled using homogeneous electric fields were determined to alter the activation barrier for O2 dissociation. The electrolyte solution was modeled using an H5O2+ cluster that allowed for proton transfer at constant charge. The first reaction step was determined to be the simultaneous proton and electron transfer to form OOH and is followed by dissociation. Each reaction step was found to be exothermic without potential corrections, which is likely to be consistent with the ORR at low potentials.; The influence of electronic structure changes induced by Pt bimetallic alloys was explored on model surfaces. Lattice strain and electronic ligand contributions were explored both individually and together on model alloys surfaces. Compressing Pt(111) was found to broaden the metal d-band, which shifts the electron density away from the Fermi level. This destabilizes the adsorption of all ORR intermediates. D-band modifications induced by ligand effects were found to be unpredictable as increasing the concentration of d-states near the Fermi level does not necessarily increase the number of states at the Fermi level.; On the Pt3M substrates that are more representative of true alloys, lattice strain was found to be the dominant effect of alloying. The enhancement in ORR activity for Pt-alloys is likely due to a compression of the Pt lattice, which destabilizes OH adsorption and increases the availability of active sites Excessive compression is likely to reduce activity due to destabilization of O2, which kinetically limits the ORR.; Calculations examining H2S decomposition on Pd bimetallic alloys were performed in a similar manner to the ORR calculations. As in the ORR study, compressive strain was found to weaken H2S adsorption and reduce the energies of the decomposition reactions. |
