Advanced Materials for Energy Conversion and Storage VII: Energy Conversion with Emphasis on SOFC
Sponsored by: TMS Functional Materials Division, TMS: Energy Conversion and Storage Committee
Program Organizers: Jung Choi, Pacific Northwest National Laboratory; Soumendra Basu, Boston University; Amit Pandey, Lockheed Martin Space; Paul Ohodnicki, University Of Pittsburgh; Kyle Brinkman, Clemson University; Partha Mukherjee, Purdue University; Surojit Gupta, University of North Dakota
Tuesday 8:30 AM
March 16, 2021
Room: RM 23
Location: TMS2021 Virtual
Session Chair: Soumendra Basu, Boston University; Amit Pandey, Lockheed Martin Space
8:30 AM
Experimental and Computational Investigations of the Multiple Impurities Effect on the SOFC Cathode Materials: Rui Wang1; Hooman Sabarou1; Yu Zhong1; 1Worcester Polytechnic Institute
On purpose of studying the multiple impurities poisoning phenomena in the SOFC cathode systems, three common cathode materials, namely (La0.8Sr0.2)0.95MnO3 (LSM), (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3 (LSCF) and La2NiO4 (LNO), were prepared, sintered and finally annealed at 1073, 1173, and 1273 K in the different impurity-containing atmosphere, respectively. By means of the X-Ray Diffraction (XRD) and the Scanning Electron Microscope (SEM) technique as well as the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) methodology, the secondary phases under different temperatures, PO2, and partial pressure of impurities were well predicted as well as experimentally verified correspondingly. Comprehensive comparisons among the three candidates under different impurity-containing conditions would also be made to provide guidance on the alternatives of the cathode materials. Finally, the accelerated tests, in some cases, were validated in our work which might also be scrutinized in the future as they may present different degradation mechanisms.
8:50 AM Invited
Characteristics of Advanced Protective Layer for SOFC Stacks: Jung Choi1; John Hardy1; 1Pacific Northwest National Laboratory
The protective coating of interconnect materials is essential in Solid oxide fuel cells (SOFCs) because of that high-temperature operation, interconnect material making chromium evaporation, and it makes cathode poisoning. To mitigate this issue, an alumina coating and a (Mn, Co)3O4-CeO spinel coating were developed at PNNL. The alumina coating provides an electrically nonconductive stable coating, and the spinel coating provides an electrically conductive and stable coating on the stack interconnects. However, the Mn-Co-O spinel contains Co, which is a relatively expensive material. Hence, if a cheaper element can be substituted, it could substantially reduce manufacturing costs. This paper summarizes recent efforts to replace Co with Ni or Cu.
9:20 AM Invited
Compositionally-stabilized Nickelate-Ceria Composite Oxygen Electrodes for Reversible Solid Oxide Fuel Cells and Electrolyzers: Srikanth Gopalan1; Jane Banner1; Ayesha Aktar1; 1Boston University
Composite electrodes consisting of a rare-earth nickelate phase and a doped rare-earth ceria phase with a high level of rare-earth doping have been investigated as oxygen electrodes. While rare-earth nickelates have shown great promise as oxygen electrodes, they are known to become unstable in contact with rare-earth doped ceria. Herein, we describe a strategy to eliminate this instability and enable the use of these electrodes as stable high performance oxygen electrodes in both SOFC and SOEC applications. The performance of such composite electrodes is explored using a symmetrical cell approach, and through the electrical conductivity relaxation (ECR) method. The symmetrical cell tests which reveal the stabilized nickelate-ceria electrodes to be superior, are also well-correlated with the results of testing complete cells in both SOFC and SOEC modes. Based on these results we propose deploying these stabilized nickelate-ceria composite electrodes as oxygen electrodes in reversible SOFC-SOEC systems.
9:50 AM
Computational Guided Investigations on LSM/YSZ Triple-phase Boundaries: Rui Wang1; Yu Zhong1; 1Worcester Polytechnic Institute
To better overcome the drawbacks of reducing the operating temperature of the lanthanum-strontium manganite (LSM) and yttria-stabilized zirconia (YSZ) cell systems, the length of triple-phase boundaries (TPBs) as well as the numbers of more active reaction site become critical. Recently, Composites of LSM and YSZ, as functional grade materials (FGMs), have been proposed to improve the electrochemical performance of LSM/YSZ. On purpose of studying the behavior of the TPBs as well as tuning better compositions of the LSM/YSZ functional layers, the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) methodology was adopted due to its ability of the high-throughput predictions of the optimized system. Meanwhile, the formation of the secondary phases can also be simulated under either operational and sintering conditions with different temperatures and PO2. Finally, an optimized ratio or concentration gradient of the LSM/YSZ composites will also be proposed to improve the SOFC performance under different conditions.
10:10 AM
In-situ Cathode Cleaning for Chromium Poisoning Recovery in Solid Oxide Fuel Cells: Zhikuan Zhu1; Michelle Sugimoto1; Srikanth Gopalan1; Soumendra Basu1; Uday Pal1; 1Boston University
A quick, cost-effective, in-situ method was developed to reverse chromium poisoning in SOFC cathodes. In this method, Cr deposits are removed from the cathode by operating the cells under mild electrolytic conditions. The method is shown to reverse chromium poisoning and recover cell performance. In the present work, cells with LSM cathodes that were degraded by exposure to Cr-containing vapors are cleaned by applying a mild electrolytic bias, as well as increasing the air and fuel humidity. Cell performance improved as a result of cleaning, as evidenced by current-voltage and EIS measurements. SEM and EDS comparisons with a poisoned cell, demonstrate significantly lower amounts of Cr in the cleaned cell. No other microstructural changes in the cathode were observed. Poisoning/cleaning cycle tests were repeated on the same cell to demonstrate feasibility of using this method a number of times during the operating lifetime of the cell.
10:40 AM
Three-dimensional Simulation of Electrochemical Impedance in Solid Oxide Fuel Cell (SOFC) Cathodes and Its Application in Cathode Characterization: Vishwas Goel1; Dalton Cox2; Scott Barnett2; Katsuyo Thornton1; 1University of Michigan; 2Northwestern University
In this work, we propose the application of electrochemical impedance spectroscopy (EIS) in characterizing the microstructure of mixed ion-electron conducting (MIEC) cathodes of solid oxide fuel cells (SOFC). In particular, we show that the EIS data can be used for determining the effective tortuosity of cathodes. We obtain the impedance response of a SOFC cathode, with an experimentally determined three-dimensional (3D) microstructure, by solving the mass conservation equation for the oxygen vacancies under the conditions of an AC load across the cathode’s thickness and surface reaction at the pore/solid interface. Our simulation results provide two key insights. First, there is a need to modify the Adler-Lane-Steele model, which is widely used for fitting the impedance behavior of a MIEC cathode, to account for the difference in the oscillation amplitudes of the oxygen vacancy concentration at the pore/solid interface and within the solid bulk. Second, the effective tortuosity is dependent on the frequency of the applied AC load as well as the material properties (reaction rate constant and bulk diffusivity), and thus the prevalent practice of treating the tortuosity as a constant for a given microstructure should be revised.