Nature of the Selenium Submonolayer Effect on the Oxygen Electroreduction Reaction Activity of Ru(0001)

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I present here results of first principles studies of the adsorption energetics of the intermediates of the oxygen electroreduction reaction (ORR) on a Se-modified Ru(0001) surface. The calculations were performed for 1/3 and 2/3 monolayer coverage of Se, as well as for clean Ru(0001) as a reference. The binding energies of O and OH on Ru(0001) are found to decrease significantly with the presence of Se, and this effect increases with the Se coverage. The Se surface modification is found not to change the Ru local density of electronic states noticeably. However, Se atoms accept electronic charge from the surface and thus become negatively charged. As a result, they repeal electrostatically the adsorbed negatively charged O and OH intermediates and in this way reduce their binding energies. This effect provides an alternative way of tuning the reactivity of the catalyst surfaces. Since for the Ru case reduction of the O and OH binding energies makes ORR energetically favorable, Se modification dramatically improves the ORR rate on Ru. Adsorption of O2 and coadsorption of the ORR intermediates and water have also been studied. The effect of coadsorption on the binding energies of O and OH are discussed.