Speaker
Description
Precipitating metallic nanoparticles from perovskite-type oxides upon applying reducing conditions is a highly promising approach to obtain oxide-supported catalysts with exceptional properties. This process is often called exsolution. On mixed ionic/electronic conducting oxide electrodes the obtained catalyst particles can be electrochemically switched between different activity states, which is a particularly interesting property of these novel catalysts.
In this work, the exsolution and re-oxidation of iron particles on perovskite-type mixed conducting La0.6Sr0.4FeO3-δ (LSF) electrodes was studied by synchrotron-based in-situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) at 625 °C in H2/H2O atmosphere. Upon cathodically polarizing the LSF electrodes – i.e. applying strongly reducing conditions – the formation of metallic α-Fe particles could be observed on the LSF surface. This change of the electrode surface chemistry was accompanied by a strong improvement of its electro-catalytic activity. In contrast, application of sufficiently high anodic polarization – i.e. oxidizing conditions – the oxidation of α-Fe to Fe1xO and Fe3O4 could be observed, accompanied by a drastic drop of the catalytic activity. This shows that re-integration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst. Rather, it is possible to reversibly switch between high and low activity state even though the exsolution process itself is irreversible.
To understand the origin of the high and low electro-catalytic activity, a mechanism is suggested which considers the different adsorption behavior of hydrogen on metallic iron and oxides. A consequence of this is that the presence of metallic iron particles establishes a novel reaction pathway that bypasses the rate limiting step on the bare oxide electrode surface, thus enabling the observed increase in electro-catalytic activity.
Short information on the speaker
Alexander K. Opitz
TU Wien, Institute of Chemical Technologies and Analytics
Getreidemarkt 9/164-EC, 1060 Vienna, Austria
Email: alexander.opitz@tuwien.ac.at
Short CV
Since Nov. 2018 Assistant Prof. at TU Wien, Institute of Chemical Technologies & Analytics, Division Electrochemistry
Feb. – Sept. 2017 Visiting Scientist at MIT, Department of Nuclear Science and Engineering, Research Group of Prof. Bilge Yildiz.
Since 2014 Head of Research Group “Electrochemical Energy Conversion”
Aug. 2011 – Oct. 2018 University Assistant at TU Wien, Institute of Chemical Technologies & Analytics, Division Electrochemistry.
Aug. 2008 – Jul. 2011 PhD study at TU Wien. Title of thesis: „Oxygen Exchange Pathways of Platinum Model Electrodes on Yttria-stabilized Zirconia“
Main Research Areas
• Electrochemistry & Solid State Ionics: Study of electrode kinetics, current pathways, and electrochemically active zones of solid state electrochemical systems, high temperature electrolysis of H2O and CO2.
• Heterogeneous Catalysis: In-situ spectroscopic and analytic studies on the surface chemistry and catalytic activity of electrodes.
• Materials Chemistry: Synthesis and characterization of novel, alternative materials for solid oxide cells.
