Solid State Electrochemistry and Electroceramics
Jürgen Fleig is mainly active in the research area called solid state ionics. This area deals with thermodynamic and kinetic properties of ionic charge carriers in solids and includes in-depth analysis of point defects which are responsible for a major part of kinetic phenomena in ionic materials. Investigations also take account of mobile electrons which are inevitably coupled to ionic defects via charge neutrality and interaction with the ambience. Thus complex materials and systems (electrochemical cells,electroceramic devices) have to be considered exhibiting temperature, voltage, and partial pressuredependent ion and electron conduction in the bulk, across or along grain boundaries and interfaces as well as at electrodes. Also from an application point of view this research area is highly dynamic particularly due to the crucial importance of many ionic materials in energy related devices: Solid electrolytes or mixed conductors are the basis of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) and also essential (as electrode and partly as electrolyte material) in lithium-ion batteries. Permeation membranes used for syngas formation or in the oxy-fuel process for CO2 sequestration are also based on ionic materials. Moreover, the closely related field of electroceramics (partly overlapping with solid state ionics) includes application of ionic ceramics as capacitors, sensors, piezoelectric actuators, etc. Hence, basic research in this field is not only relevant from a fundamental point of view but also of high technological or societal relevance.
Two kinetic processes are in the focus of Jürgen Fleig’s research group: Ion motion in oxides and electrochemical electrode reactions at oxide/gas interfaces (e.g. oxygen reduction kinetics). In the laboratory of Jürgen Fleig several improved methods have been developed for investigating these processes for example by means of micro-(patterned) electrodes: This enabled analysis of single grain boundaries in polycrystalline solids, spatially resolved measurements on inhomogeneous ceramics and in particular highly flexible measurements of electrochemical electrode properties: Numerous mechanistic information regarding the oxygen reduction kinetics on oxides could be obtained. Also investigation of charge transport in thin films strongly benefited from novel electrode geometries. Recently, collaboration with H. Hutter (TU Vienna) lead to a further broadening of the experimental approach used to analyze kinetic processes in/on oxides by also employing secondary ion mass spectrometry (SIMS) analysis. Particularly 18O tracer experiments under electric field turned out to be highly attractive for monitoring electrochemically active electrode sites and for diffusion studies on thin films. Finally, collaborations with several other partners give access to important additional surface analytical tools such as XPS, AES or in-situ online analysis of eluates by ICP-OES.