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Photo-Oxidation of Water on Defective Hematite(0001)
journal contribution
posted on 2015-02-06, 00:00 authored by Manh-Thuong Nguyen, Simone Piccinin, Nicola Seriani, Ralph GebauerDefects are unavoidable and usually
originate exotic properties
in realistic materials. One of the most fundamental defect-induced
properties of a solid surface is its reactivity to adsorbed species.
Defects in anodes of electrochemical cells for water splitting could
therefore play a critical role in the interatomic interactions at
the solvent/solid interfaces and hence in determining the catalytic
properties of these materials. Here, by means of density-functional
calculations at the PBE+U level, we investigate photo-oxidation of
water on defective hematite(0001) substrates which accommodate intrinsic and extrinsic point defects,
namely, Fe and O vacancies, as well as N substitutional impurities.
In this work, the water oxidation process is assumed to be driven
by the redox potential for photogenerated holes with respect to the
normal hydrogen electrode. Although iron vacancies do not reduce the
overpotential, oxygen vacancies and N impurities lower the overpotential
by 0.2–0.3 V compared to the ideal case. These changes are
attributed to the coordination loss or the substitution-induced charge
states of surface atoms that modify the electronic structure of the
surface, thus affecting the relative stability of adsorbed intermediates.