SOFC; 3D-microstructure; Mixed Ionic Electronic Conductor MIEC; FIB-tomography; cathode activity
Pecho Omar, Holzer Lorenz, Yang Zen, Martincuk Julia, Hocker Thomas, Flatt Robert J., Prestat M. (2015), Influence of strontium-rich pore-filling phase on the performance of La0.6Sr0.4CoO3−δ thin-film cathodes, in Journal of Power Sources
, 274, 295-303.
Holzer Lorenz, Iwanschitz Boris, Hocker Thomas, Keller Lukas, Pecho Omar, Gasser Philippe, Münch Beat, Sartoris Guido (2013), Redox cycling of Ni-YSZ anodes for Solid Oxide Fuel Cells: Influence of tortuosity, constriction and percolation factors on the effective transport properties, in Journal of Power Sources
, 242, 179-194.
Gaiselmann G, Neumann M, Holzer L, Hocker T, Prestat MR, Schmidt V (2013), Stochastic 3D modeling of La0.6Sr0.4CoO3-delta cathodes based on structural segmentation of FIB-SEM images, in COMPUTATIONAL MATERIALS SCIENCE
, 67, 48-62.
Gaiselmann Gerd, Neumann Matthias, Holzer Lorenz, Hocker Thomas, Prestat Michel Rene, Schmidt Volker (2013), Stochastic 3D modeling of La0.6Sr0.4CoO3-delta cathodes based on structural segmentation of FIB-SEM images, in COMPUTATIONAL MATERIALS SCIENCE
, 67, 48-62.
Pecho Omar, Prestat Michel, Yang Zen, Hwang Jong, Son Ji-Wu, Holzer Lorenz, Hocker Thomas, Martinjuck Julia, Gauckler Ludwig (2012), Microstructural and electrochemical characterization of thin La0.6Sr0.4CoO3-δ cathodes deposited by spray pyrolysis
Gaiselmann Gerd, Neumann Matthias, Pecho Omar, Hocker Thomas, Schmidt Volker, Holzer Lorenz, Quantitative Relationships between Microstructure and Effective Transport Properties based on Virtual Materials Testing, in AIChE Journal
Holzer L., Wiedenmann D., Münch B., Keller L., Prestat M., Gasster P., Robertson I., Grobéty B., The influence of constrictivity on the effective transport properties of porous layers in electrolysis and fuel cells, in Journal of Materials Science
Solid Oxide Fuel Cells (SOFC) are efficient energy converters that emit smaller amounts of CO2 than most currently available hydrocarbon-fueled combustion techniques. In addition they can be adapted to a variety of fuels and might be the missing link to ‘clean’ coal energy production. A high cathode activity at intermediate operating temperatures (500°C-600°C) is one of the most important goals that must be reached for successful market entry with modern SOFC architectures (e.g. micro-SOFCs). Thereby, mixed ionic-electronic conductors (MIEC) such as LaxSr1-xCoO3-d (LSC), have advantageous properties (e.g. high surface exchange coefficient) which will contribute to a high cathode activity. However, in addition to the intrinsic material properties, also microstructure effects on the various electrode processes (oxygen exchange by dissociative adsorption and incorporation, bulk and surface diffusion, gas diffusion, charge trans-fer reactions) play a very important role for the cathode kinetics. Thereby, nanotechnology opens new possibilities for improved electrode microstructures, e.g. by the use of nano-particles synthesized in a plasma or by the fabrication of nano-porous thin films. Based on these options a very large variation of different cathode microstructures can be pro-duced, e.g. by a combination of materials with different intrinsic properties (MIEC/LSC and pure ionic conductor/GGO or YSZ), with different particle sizes (from nano- to micro-sized) and due to variable compositions with different solid volume fractions (and porosity). To this end, a fundamental understanding of the complex relationships between 3D-micro-/nanostructures and the corresponding cathode reactions is not yet established on a systematic (quantitative, sta-tistical) basis.The proposed project thus aims at investigating, on a fundamental level, the microstructure influence on the oxygen re-duction kinetics in intermediate temperature solid oxide fuel cells (SOFC). So far the possibilities which arise from a combination of multi-physical modeling with quantitative microstructure analysis have only been exploited to a limited extent in SOFC research. In a multidisciplinary approach involving ceramics processing, experimental electrochemistry, 3D-microstructure analysis and various modeling techniques we intend to bring to the fore the effect of first order and higher order topological parameters on the electrode activity. More specifically, we aim at establishing quantitative cor-relations between the kinetics-relevant structural parameters, spatial distribution of mass and charge fluxes and cathode activity. The project includes a) an experimental- and performance-oriented part (Ph.D.) and b) a theory- and modeling-oriented part (Post Doc). In the experimental part a wide range of different microstructures (including nanoparticles from flame spray synthesis, nano-porous thin films, nano-composites with CGO backbone) will be investigated for cathodes that are based on La0.6Sr0.4CoO3-d mixed conductor. Thereby, the relationships between 2D- and 3D-topological parameters with the electro-chemical and transport related cathodic losses will be established in a systematic and quantitative way. Based on these relationships, new microstructure concepts for improved cathode activity shall be established.In the theoretical part, the coupled cathode processes shall be simulated on a microstructure scale using the finite ele-ment method (FEM). These simulations are based on high resolution 3D-models from FIB-tomography or from stochas-tic modeling which represent the thickness of the entire cathode layer. Furthermore, the kinetics of the oxygen adsorp-tion, surface and bulk diffusion shall be explored by ab-initio calculations using density functional theory (DFT). This information is then used for a refinement of the kinetic description in the FE-Model. In this way the microstructure modeling can be linked with atomistic considerations, but also with 3D topology analysis and with experimental elec-trochemistry. Significant synergies are expected between the experimental and theoretical investigations.The strength and the originality of the proposed project is based on novel combinations of cutting-edge methodologies such as stochastic modelling, FIB-nanotomography and 3D-topology theory, or the link between finite element analysis on a microstructural scale with ab-inito DFT calculations. Thereby the project can profit from a high methodological know how which was established systematically over the last years. The outcome will be a fundamental understanding about the complex relationships between topological features, local electrochemical activity, transport mechanisms (gas, ions, electronic) and overall reaction kinetics. On a longer term the fundamental understanding and know-how acquired during this project should be utmost useful for the development of optimized microstructures with enhanced electro-chemical performance.