Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 18: Focus Session: Frontiers in Reducible Oxide Surface Science II

O 18.8: Vortrag

Montag, 12. März 2018, 17:30–17:45, HE 101

identification of active sites for water oxidation with extremely low overpotential on multicomponent spinel Co_xNi_1−xFe₂O₄(001) surfaces — •hamidreza hajiyani and rossitza pentcheva — Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen

Using density functional theory calculations with an on-site Hubbard term (DFT+U) we explore the effect of cation substitution and surface termination on the performance of Co_xNi_1−xFe₂O₄(001) as an anode material in the oxygen evolution reaction (OER). To identify the active sites, we investigated the performance of different reaction sites (Fe, Co, Ni and O) at the B-layer with 5-fold coordinated Co/Ni and with an additional 0.5 ML Fe at the (001) spinel surface. Our results indicate that mixing of Co and Ni in equal concentrations (x=0.5) lowers the overpotential over the end members for the majority of reaction sites. Comparison of the overpotentials indicates that surface Co cations on the 0.5 ML Fe termination are the most active sites with the lowest theoretically reported overpotential of 0.30 V. We have shown that this beneficial performance correlates with the modification of the binding energies of intermediate species to the surface. Analysis of the electronic properties and spin densities indicate that the oxidation state of Fe changes from +3 in the bulk to +2 on the 0.5 ML Fe surface, while Co and Ni cations at this termination preserve the bulk oxidation states of +2. Funding by the DFG within SPP1613 is gratefully acknowledged.