Research Report 2020
1.7
Institute of Computational Physics
Model Based Optimization of CGO-Ni Based SOFC Anodes
Costs and lifetime are currently the limiting factors for a broader use of Solid Oxide Fuel Cells (SOFC) with natural gas for combined heat and power. Therefore, a systematic optimization of materials and cell-concepts is needed to enable the use of cheaper components and to increase lifetime and efficiency. In our approach we build on digital materials design (DMD), whereby methods for multiphysics simulation, 3D microstructure characterization (tomography data) and electrochemical impedance spectroscopy (EIS) are combined. Based on the DMD approach, the relations between material properties, microstructure, cell-design and performance are established on a quantitative level. This approach helps to define design guidelines for optimized electrodes and accelerates the innovation cycle for future SOFC devices. Contributors: Partner(s): Funding: Duration:
P. Marmet, L. Holzer, T. Hocker, J. Brader, J. Grolig, H. Bausinger, A. Mai Hexis Swiss Federal Office of Energy 2019–2022
For the next generation of SOFC cells, the requirements of the market call for higher efficiency, longer lifetime and lower system costs. In order to meet these requirements we elaborate on new anode concepts, which are based on doped ceria with nickel combined with cheap ferritic interconnectors. However, complex physico-chemical processes are involved including transport of gas in the pores, transport of ions and electrons in the ceria phase, fuel oxidation reaction on the surface of ceria etc. Hence, there are numerous conflicting requirements, which complicate the development process. Therefore, sophisticated methods including mathematical models as well as experimental methods are needed for a systematic optimization of the system.
simulation of the EIS-spectra as well as the DC behaviour during the normal cell operation. Therewith, a basic understanding of the complex physicochemical processes and a deconvolution of the EISspectra is achieved. A calibrated simulation model is then used to predict the impact of design adjustments (e.g. material and microstructure variations) on the cell performance. A key point thereby is to include the effects from microstructure appropriately in the model.
Fig. 2: Potential drop along an anode microstructure to determine the effective conductivity using GeoDictŠ.
Microstructure analysis based on FIB-tomography enables to quantify morphological characteristics (tortuosity, porosity etc) and the associated transport properties. With the digital materials design (DMD) approach, the effect of microstructure variation on the cell performance can be assessed. By establishing the relation between material properties, microstructure, cell-design and performance, guidelines for a new anode materials design can be deduced. This allows for a faster and more systematic development of new SOFC electrodes.
Fig. 1: Deconvolution of the simulated anode EIS-spectra: ZHOR = hydrogen oxidation reaction impedance, Ztransport = charge carrier transport imped., Zgas = gas imped., Zanode,tot = total anode imped.
In SOFC research, electrochemical impedance spectroscopy (EIS) is an essential characterization tool, which serves as a basis for materials optimization on the electrode, cell and stack levels. However, overlapping processes in the EIS spectra and lacking knowledge about the detailed physico-chemical processes makes it difficult to interpret the EISspectra correctly. Multi-physics simulation models developed at ICP with AC and DC modes, enable the
Zurich University of Applied Sciences
8
www.zhaw.ch
