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Publication type:	Doctoral thesis
Title:	Digital materials design of solid oxide fuel cell anodes
Authors:	Marmet, Philip
Advisors / Reviewers:	Holzer, Lorenz Hocker, Thomas Joseph, Brader
DOI:	10.21256/zhaw-28430
Extent:	xix, 419
Issue Date:	2-Aug-2023
Publisher / Ed. Institution:	University of Fribourg
Publisher / Ed. Institution:	Fribourg
Language:	English
Subjects:	Solid Oxide Fuel Cell (SOFC); Digital materials design; Titanate; CGO; Ceramic fuel electrode; Virtual materials testing; Stochastic geometry; Microstructure modeling; Pluri-Gaussian method; Microstructure characterization; Composite conductivity; Multiphysics multiscale modeling; Effective property; Mixed Ionic Electronic Conductor (MIEC); Electrochemical impedance spectroscopy; Impedance response modeling; Noble metal catalyst; GeoDict; FIB tomography; Renewable energy; Energy conversion and storage; Microstructure optimization
Subject (DDC):	621.3: Electrical, communications, control engineering
Abstract:	The storage and efficient conversion of energy is one of the key issues for a successful transition to renewable energies. Solid oxide cell (SOC) technology is a promising solution for the conversion of electrical energy to storable chemical energy (power-to-gas) in the solid oxide electrolysis cell (SOEC) mode, and for the on-demand supply of electrical energy using synthetic gas or biogas (or natural gas) as input in the solid oxide fuel cell (SOFC) mode. To significantly improve on the unavoidable degradation of state-of-the-art anodes like Ni-YSZ, we elaborate on new nickel-free electrode concepts, which are based on mixed ionic and electronic conductors (MIEC) like doped ceria and perovskite (e.g., titanate) materials. However, the anode performance is governed by complex physico-chemical processes including transport of gas in the pores, transport of ions and electrons in both solid phases and fuel oxidation reaction on the surface of the MIECs, which are not yet fully understood. Hence, there are numerous conflicting requirements and lack of knowledge complicating the development and optimization process. These challenges are addressed in this thesis in two ways. First, a Digital Materials Design (DMD) framework for the systematic and model-based optimization of MIEC SOC-electrodes is elaborated. In our DMD approach we combine stochastic microstructure modeling, virtual testing of 3D microstructures and a multiscale-multiphysics electrode model to explore the available design space by performing parametric studies. The basis for the DMD process is a set of fabricated solid oxide cells. Their real microstructures are reconstructed using FIB-SEM tomography. Stochastic digital microstructure twins with matching microstructure properties are then constructed for each real structure using a pluri-Gaussian method. On that basis, the microstructure can be virtually varied for a large parameter space in a realistic way. The real and subsequently the virtual 3D structures need to be characterized quantitatively by means of image analysis and numerical simulations. Hence, a standardized and automated microstructure characterization has been developed, which enables the fast determination of an extensive set of microstructure properties relevant for SOC electrodes. Moreover, specific microstructure properties like the ‘composite conductivity’ crucial for novel composite MIEC electrodes are introduced and discussed. A multiphysics continuum simulation model is then used to predict the impact of the microstructure variation on the electrode performance, using the previously determined microstructure properties as an input. In addition, the kinetic reaction parameters of the model are calibrated to the experimental performance characterizations of the cells (e.g., EIS results). This model-based performance prediction enables to establish the relationship between materials choices and compositions, fabrication parameters, microstructure properties and cell-performance. Due to the integration of stochastic modeling (pluri-Gaussian method) and its combination with automated characterization and model-based performance prediction, the number of the involved 3D microstructures can be significantly increased. This approach is thus capable to explore a much larger design space than it would be possible with experimental methods only. On this basis, design guidelines for the fabrication of electrodes with improved performances can be provided, which closes the loop of this iterative workflow. This DMD workflow is made available for the research community by the release of two software apps for the standardized microstructure characterization and stochastic microstructure modeling for SOC electrodes. Detailed information on these methodologies is also provided by the corresponding publications. Second, this DMD workflow is applied for the optimization of titanate based LSCT-CGO SOFC-anodes with a noble metal catalyst impregnation. Based on the performance and microstructure characterization of fabricated cells, several DMD studies are performed. Thereof, design guidelines for titanate-CGO anodes are provided including different microstructure design concepts and parameter specifications like appropriate material compositions and porosity. Moreover, the new opportunities as well as the current limitations of these nickel-free electrodes are discussed in great detail.
Further description:	This PhD-Thesis was presented to the Faculty of Science and Medicine of the University of Fribourg (Switzerland) in consideration for the award of the academic grade of Doctor of Philosophy in Physics (Thesis No: 5369). The doctorate was mainly pursued at the Institute of Computational Physics ICP at Zurich University of Applied Sciences ZHAW in Winterthur, Switzerland PhD Presentation: https://zhaw.mediaspace.cast.switch.ch/mediashare/d430305eb29a01af/media/t/0_8py1hjfn GeoDict User Meeting 2021 Presentation: https://www.youtube.com/watch?v=AIROVKq5yoc
URI:	https://digitalcollection.zhaw.ch/handle/11475/28430
Related publications:	https://doi.org/10.1039/D1CP01962G https://doi.org/10.1039/D3YA00132F
Related research data:	https://doi.org/10.5281/zenodo.7741305 https://doi.org/10.5281/zenodo.7744110
License (according to publishing contract):	Licence according to publishing contract
Departement:	School of Engineering
Organisational Unit:	Institute of Computational Physics (ICP)
Published as part of the ZHAW project:	Versatile oxide fuel cell microstructures employing WGS active titanate anode current collectors compatible to ferritic stainless steel interconnects (VOLTA) GeoCloud – Simulation Software for Cloud-based Digital Microstructure Design of New Fuel Cell Materials
Appears in collections:	Publikationen School of Engineering

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