Berlin 2018 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 24: Focus Session: Structure and Chemistry of Metal-Oxide Surfaces I
O 24.5: Hauptvortrag
Dienstag, 13. März 2018, 11:45–12:15, MA 005
Potential-Specific Structure at the Hematite-Electrolyte Interface — Martin E. McBriarty1, Joanne E. Stubbs2, Peter J. Eng2, Guido von Rudorff3, Jochem Blumberger3, and •Kevin M. Rosso1 — 1Pacific Northwest National Laboratory, Richland, WA, USA — 2Argonne National Laboratory, Lemont, IL, USA — 3University College London, Bloomsbury, London, England, UK
The structure of transition metal oxide interfaces with aqueous electrolyte regulates the reactions fundamental to (photo)electrochemical energy conversion and electrode degradation. Measurements that provide atomically precise structural models of ion and solvent arrangements are essential, but most rely on static conditions not operating conditions far from equilibrium. Using a novel cell, the structure of the hematite (α-Fe2O3) (1-102)-electrolyte interface was measured under controlled electrochemical bias using synchrotron crystal truncation rod X-ray scattering. At increasingly cathodic potentials, charge-compensating protonation of surface oxygen groups increases the coverage of bound water while adjacent water layers displace outwardly and became disordered. Returning to open circuit potential leaves the surface in a persistent metastable state. Thus, the flux of current and ions across the interface is regulated by multiple electrolyte layers whose structure changes in the applied potential. The study reveals the complex environment underlying the simplified electrical double layer models used to interpret electrochemical measurements and emphasizes the importance of condition specific structural characterization for properly understanding catalytic processes at these interfaces.