Publication date: 10th April 2024
Surfaces of mixed ionic and electronic conducting oxides play a crucial role in energy conversion technologies as they provide a high catalytic activity for different reactions, such as oxygen reduction, oxygen evolution, or (photo)electrochemical water splitting [1]. Enhancing and optimizing these surfaces by various strategies is thus a highly active research field. Recent studies have revealed that even sub-monolayer amounts of surface modifications fundamentally alter the properties of mixed conducting surfaces, affecting both work function and catalytic activity [2],[3],[4]. A comprehensive understanding of these effects would greatly facilitate the targeted optimization of materials and devices, but detailed mechanisms and the roles of specific charge carriers and defects are largely subject of speculation.
In this contribution we discuss our recent results on the effects of two major types of surface modifications: acidic adsorbates from gaseous impurities and ultra-thin oxide decoration layers. We studied their effects on the catalytic activity for oxygen exchange on pristine thin film surfaces by in-situ impedance spectroscopy during pulsed laser deposition (i-PLD) and investigated the atomic-scale processes that are induced by these surface modifications by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) [5].
Our study shows that surface modifications alter the properties of mixed conducting surfaces for oxygen exchange systematically based on the ionic potential or the acidity of both modification and host material’s surface. As the fundamental mechanism for sub-monolayer surface modifications, we could identify charge redistribution processes and dipole formation between the mixed conductor and the modification. Our results further emphasize the redox activity of oxygen on mixed conducting surfaces and the complicated role of point defects at oxide interfaces. Based on our results, we present a tentative, but comprehensive theory for the effects of surface modifications on mixed conducting surfaces to further push the search for ideal material combinations for specific catalytic reactions.
The authors like to acknowledge the financial support and open access funding provided by the Austrian Science Fund (FWF) project P31654-N37 as well as project funding by the Austrian Research Promotion Agency (FFG) for the project ELSA. M.S. gratefully acknowledges support from a Max Kade Fellowship of the Max Kade foundation. This research has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation programme, grant agreement no. 755744/ERC-Starting Grant TUCAS.
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