Energy Materials 2017: Materials for Energy Conversion with Emphasis on SOFC: Session I
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
Monday 8:30 AM
February 27, 2017
Location: San Diego Convention Ctr
Session Chair: Amit Pandey, LGFCS
8:30 AM Introductory Comments
8:40 AM Invited
Low Temperature RAA Process for SOFC Stacks: Jung Pyung Choi1; Jeffry Stevenson1; 1Pacific Northwest National Laboratory
Chromia-forming ferritic stainless steels are preferred interconnect materials for intermediate temperature SOFCs because of their resistance to oxidation and low cost. However, they produce Cr-containing volatile species at SOFC operating temperatures, which can cause cathode poisoning. Hence, a protective coating is required on the surface of metal interconnect material. Reactive Air Aluminization (RAA) method was developed and used for the protective coating for prohibit chrome poisoning in the cathode material and for eliminating or minimizing reaction in between sealing material. This RAA process is typically done by 1,000°C for forming stable alpha-alumina phases on the stainless steel surface. However, industrial partners want to reduce processing temperature. From this presentation, we will report the progress of developing lower temperature RAA process. We found potential that process temperature can be reduced at least 50°C or more.
Oxygen Reduction Reaction Mechanisms on Ruddlesden-Popper Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells: Wenyuan Li1; Bo Guan1; Xinxin Zhang1; Xingbo Liu1; 1West Virginia University
Ruddlesden-Popper (R-P) phases have been investigated widely as IT-SOFC cathodes. ORR mechanism for R-P phase is investigated using (LaSr)2NiO4±δ as example. The governing factors of ORR are identified as oxygen adsorption and incorporation based on the findings in reaction orders, stoichiometry-related chemical capacitances and intrinsic anisotropic properties. The incorporation rate depends on the amount of interstitial oxygen. Since the unfilled interstitial sites in R-P phase serve to accommodate the adsorbed oxygen during incorporation, like vacancies in the perovskite, more oxygen interstitial would seem to suppress the kinetics of this process. In regard to this, a physical model is proposed to reconcile the discrepancy between the experimental results and intuitive reasoning. This model explains how oxygen interstitial works to regulate the exchange rate, and the contradiction between oxygen vacancy and oxygen interstitial is harmonized so that the latter in the R-P structure also positively promotes the incorporation rate in ORR.
9:25 AM Invited
Oxygen Reduction Reaction at the Cathode of Solid Oxide Fuel Cell Enhanced with Oxide Particles: Changrong Xia1; 1University of Science and Technology of China
Perovskite oxides such as lanthanum strontium cobalt ferrite are mixed electron-ionic conductors that have potential application as the electrocatalysts for oxygen reduction reaction in solid-state electrochemical devices including solid oxide fuel cells (SOFCs) for efficient energy conversion and membrane reactors for clean coal energy delivery. This work presents the kinetic enhancement through various oxides; doped ceria, barium carbonate, strontium oxide, calcium oxide, and transition metal oxides. For example, BaCO3 is demonstrated to to be effective in enhanceing the high temperature oxygen reduction reaction. At 700 °C, the area specific surface resistance for La0.8Sr0.2FeO3(LSF) on yttria-stabilized zirconia electrolyte decreases from 2.95 Ω cm2 to 0.77 Ω cm2 when 12.9wt% BaCO3 nanoparticles are infiltrated to the porous LSF electrode. By comparing the improving factors reported in the literatures, it is found that the catalytic activity is even higher than those for precious metals such as Pd, Rh, Pt and Ag.
9:50 AM Break
Analysis of the Effects of Chromium Poisoning on LSM-based Cathode Using Polarization Modeling and Impedance Measurements: Ruofan Wang1; Manuel Würth2; Boshan Mo1; Uday Pal1; Srikanth Gopalan1; Soumendra Basu1; 1Boston University; 2Technische Universität München
Anode-supported planar solid oxide fuel cells (SOFCs) with yttria-stabilized zirconia electrolyte and Sr-doped LaMnO3 (LSM)-based cathode, were electrochemically tested with and without the presence of chromia-forming alloy interconnect. Humidified hydrogen (97% H2 - 3% H2O) and oxygen-nitrogen-water vapor mixture were used on the anode and cathode sides, respectively. The water vapor content on the cathode side was varied in order to control the rate of Cr vaporization. Current-voltage (I-V) and impedance spectroscopy measurements were used to characterize the performance and model the polarization losses in the cell. The role of Cr poisoning resulting in the performance degradation of the LSM-based cathode under various conditions was analyzed. The effectiveness of protective spinel coatings over the alloy interconnect in mitigating Cr poisoning of the cathode was also investigated.
Enhanced Performance of Doped Ceria Electrolyte by the Addition of Barium Carbonate in Solid Oxide Fuel Cells: Tao Hong1; Devin Harkins1; Kyle Brinkman1; 1Clemson University (CU)
Barium carbonate was added to doped ceria, Gd0.2Ce0.8O2-δ (GDC) electrolyte to improve the electrochemical performance in solid oxide fuel cells. With the addition of 5 wt% BaCO3, GDC reacts with BaCO3 to form BaCe0.8Gd0.2O3-δ (BCG) at 1000oC. In this new Ba-GDC electrolyte, BCG phase improves the sintering activity of GDC to get larger grain size and higher density. When La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) was employed as the cathode, the polarization resistance of LSCF had been reduced to half of original value. For example, at 600 and 700 oC, the resistance was reduced from 2.49 and 0.23Ωcm2 to 1.21 and 0.12Ωcm2, respectively. Compared to conventional research on cathode materials and structure, this method provides a convenient way to improve cathode performance by modifying the electrolyte.
Mitigation of Chromium Poisoning in Solid Oxide Fuel Cells: Jeffrey Fergus1; 1Auburn University
One of the challenges in the development of solid oxide fuel cells with the lifetimes needed for cost-effective implementation is avoiding the degradation in performance associated with deposition of chromium poisoning in the cathode. The source of chromium is volatilization from the alloys used for interconnects and in the balance of plant. The amount of chromium deposited in the cathode, and thus the amount of degradation in performance, can be reduced through alloy design, the application of coatings and the implementation of chromium capture systems. In this paper the strategies for mitigating chromium poisoning in solid oxide fuel cells will be discussed.