Energy Materials 2017: Materials for Energy Conversion with Emphasis on SOFC: Session III
Sponsored by: Chinese Society for Metals
Program Organizers: Amit Pandey, LG Fuel Cell Systems Inc.; Kyle Brinkman, Clemson University; Teruhisa Horita, AIST; Minfang Han, China University of Mining and Technology, Beijing
Tuesday 8:30 AM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Soumendra Basu, Boston University; Teruhisa Horita, AIST
8:30 AM Invited
New Materials for Solid Oxide Fuel Cells: Shriram Ramanathan1; 1Purdue University
Solid oxide fuel cells offer potential for direct utilization of hydrocarbons in electrochemical energy generation. I will discuss opportunities for new materials to be incorporated into solid oxide fuel cells, particularly the use of narrow gap semiconductors. Traditional ion conductors such as Y-doped zirconia possess excellent chemical stability in extreme oxygen gradients, however ion conductivity is limited by extrinsic dopant concentration. We ask the question can one design ion conductors where substitutional doping does not set the constraint for enhancing ionic transport? We explore the use of oxide electronic conductors instead of wide gap insulators and by suppressing electronic conduction by many body effects realize superior ion conductors with nearly unity transference. I will present recent results on this topic, and the briefly discuss on-going efforts to combine fuel cells with energy storage devices to design hybrid systems.
8:55 AM Invited
Investigation on Cathode Interlayer and Electrolyte for Improving Electric Power Efficiency of SOFCs: Takaaki Somekawa1; Yoshio Matsuzaki1; Yuya Tachikawa2; Hiroshige Matsumoto2; Shunsuke Taniguchi2; Kazunari Sasaki2; 1Tokyo Gas Co., Ltd.; 2Kyushu University
SOFCs can potentially achieve a generating efficiency of higher than 60%LHV. To enhance generating efficiency of SOFCs, we have investigated the materials of cathode interlayer and electrolyte in terms of reducing the internal resistances. In the conventional SOFCs, ceria-based materials are used as the interlayer. However, highly resistive solid solutions have been reported to sometimes form at the interface of interlayer/electrolyte, resulting in decreasing of the generating efficiency. In this study, we examined the effect of dopant species in ceria on the thickness of the solid solutions. The thickness of the solid solution was found to depend on the dopant species, indicating that the internal resistance will be controlled by the selection of the dopant element. In terms of electrolyte materials, the electrochemical properties of proton-conducting electrolyte materials were also investigated. The proton-conducting electrolyte with high proton-transport number was found to have the potential to significantly improve electrical efficiency.
9:20 AM Invited
Poisoning Mechanism and Performance Degradation at SOFC Cathode/Electrolyte Interfaces: Teruhisa Horita1; Masahiro Ishiyama1; Katherine Develos-Bagarinao1; Haruo Kishimoto1; Katsuhiko Yamaji1; 1AIST
Poisoning is one of the critical issues to commercialize the durable and long-term stable SOFC systems. So far, Cr- and S- poisoning are the main impurities that affect the cathode performances. Especially at the (La,Sr)(Co,Fe)O3/CeO2/ZrO2 interfaces, a significant amount of SrCrO4 and SrSO4 are formed at the grain surfaces or triple phase boundaries which affects the reaction rates for oxygen reduction as well as O2- diffusion rates inside the (La,Sr)(Co,Fe)O3 due to loss of oxygen vacancies. Also, Sr diffusion through CeO2 and formation of SrZrO3 was observed at the CeO2/ZrO2. In this presentation, poisoning mechanisms are reviewed and related performance electrochemical degradation are discussed. The prospect for the life time estimation is also discussed.
Phase Field Modelling of Microstructure and Conductivity Evolution of SOFC Electrodes: Yinkai Lei1; Tianle Cheng1; Youhai Wen1; 1National Energy Technology Laboratory
Understanding grain coarsening is important to mitigate the degradation of SOFC electrodes. In this work, we developed a phase field model to simulate the microstructure evolution of SOFC electrodes. The interfacial energy in this model can be easily tuned and two sets of energetic parameters for anode and cathode were developed respectively. Using these parameter sets, the contact angles at triple junctions in SOFC electrodes were calibrated and the grain coarsening of SOFC electrodes were investigated. The time evolution of TPB density, surface area density, grain size and tortuosity of different phases were analyzed. Furthermore, the bound charge successive approximation algorithm was used to calculate the effective conductivity of electrode at different time. The relation between the time evolution of microstructure and conductivity were discussed.
10:00 AM Break
Reactive Synthesis of Spinel Contact Layers with Metallic Precursor Powders: Jiahong Zhu1; Yutian Yu1; 1Tennessee Technological University
Electrically-conductive spinels have been extensively studied as the interconnect coating material for solid oxide fuel cell (SOFC). Furthermore, they are also being considered for the SOFC cathode-interconnect contact application. This presentation will report the sintering behaviours of several spinels with metallic precursor powders. The precursor powders are screen printed onto the Crofer 22 APU interconnect substrate, followed by sintering in air to achieve a spinel-based contact layer. The phase purity and microstructure of the sintered layers are characterized with X-ray diffraction, optical microscopy, and scanning electron microscopy. In addition, the area-specific resistance and mechanical bond strength of the sintered layers in an interconnect/spinel layer/cathode assembly is experimentally determined. The factors affecting the spinel formation via reactive synthesis with metallic precursor powders are analyzed and the underlying mechanism is elucidated.
10:40 AM Invited
Electrophoretically Deposited Copper Manganese Spinel Coatings for Interconnections in Solid Oxide Fuel Cells: Zhihao Sun1; Srikanth Gopalan1; Uday Pal1; Soumendra Basu1; 1Boston University
Chromium poisoning of the cathode of solid oxide fuel cells (SOFC) due to oxidation of metallic interconnections and subsequent formation of vapor phase chromium containing species is a well-known problem. The application of ceramic coatings on the interconnections to prevent this deleterious phenomenon is currently being extensively investigated. Copper manganese spinel coatings were deposited on Crofer 22 APU substrates by electrophoretic deposition (EPD), and subjected to a thermo-mechanical treatment for densification. The weight gain of the coated Crofer 22 APU samples under oxidizing conditions was measured using thermogravimetry. The area specific resistance (ASR) of the coated samples was measured as a function of temperature. The evolution of the microstructure of these coatings will be discussed, and related to the their effectiveness as a diffusion barrier.
Synthesis and Characterisation of Perovskite Type Anode Material and Its Tape Casting for IT-SOFC Application: Subhajit Pan1; Ramesh Biswal1; Koushik Biswas1; 1IIT Kharagpur
Solid oxide fuel cell (SOFC) is very popular nowadays because of its high efficiency, fuel flexibility, long-lasting and eco-friendly energy conversion device. Till date, yttria stabilized zirconia (YSZ) system has been dominated in the SOFC world in which Ni/YSZ cermet is commonly used as anode material. But Ni/YSZ cermet anodes shows, carbon deposition and rapid performance degradation when hydrocarbon fuels are used. Alternative perovskite systems La1-xSrxCr1-yMyO3-δ (M: Mn, Fe, and V) have attracted much attention as anode material due to their high-temperature stability, low carbon deposition, and high catalytic activity. In the present work, La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) is synthesized by solid state synthesis method. Compatibility of the anode material with perovskite electrolyte (La1-xSrxGa1-yMgyO3-δ ) is evaluated by XRD analysis, SEM, impedance spectroscopy and 4-probe method. Using an organic solvent-based formulation, flexible and homogeneous LSCM tapes were cast for potential use as an anode in SOFC.
11:25 AM Invited
Modified SOFC Cermet Anodes for Improved Catalysis at High Fuel Utilization: Paul Gasper1; Yanchen Lu1; Uday Pal1; Soumendra Basu1; Srikanth Gopalan1; 1Boston University
This research analyzes the effects of various nickel infiltration (vapor and liquid phase) processes on the performance of anode-supported SOFCs over a wide range of hydrogen and water vapor partial pressures at intermediate temperatures (600-800 Celsius). The efficacy of various infiltration techniques, resulting density and location of the sub-micron size Ni deposits, impact of the increased three-phase-boundary (TPB) length, and the stability of the deposited Ni particles were examined through long-term and/or accelerated testing. Cell performance was measured using I-V and EIS techniques, and the anodic polarization losses were calculated using a validated full cell model. Anode microstructure including the location, size and distribution of the sub-micron size Ni particle deposits was characterized employing FIB, SEM and TEM. The results identify the role of the size and location of the sub-micron size nickel particles in enhancing the anode performance at high fuel utilization.