CCS and Power Systems

Advanced Energy Systems - Solid Oxide Fuel Cells


SECA Core Technology Program - PNNL


Performer: Pacific Northwest National Laboratory

Project No: FWP-40552


Accomplishments


  • Commissioned second generation stack test fixture.

  • Successfully assembled and tested 3-cell stack fixture for long-term (approximately 6,000 hours) evaluation/validation of manganese-cobalt (M-C) spinel and alumina coated interconnects.

  • Demonstrated excellent electrical performance of M-C spinel-coated AISI 441 for over two years (20,000 hours).

  • Evaluated performance of coatings with reduced (or zero) cobalt content.

  • Optimized ultrasonic spray process for interconnect coatings. An ultrasonic spray process was evaluated and successfully developed for the application of cerium oxide-modified M-C coatings aluminization on metallic interconnects.

  • Conducted a microscopic study which included evaluation of interconnect coatings using composition and phase analysis. It was determined after one year that the oxide scale under the coating consisted of a continuous matrix of titanium-doped chromium oxide with dispersed grains of manganese-chromium oxide. No evidence of impending degradation was found using high-resolution transmission electron microscopy provided by Carnegie Mellon.

  • Completed the ASME SOFC design basis document. This living document, modeled after those published by the ASME, acts as a repository for the current best practices in the design of structurally-sound SOFC stacks. The baseline version of the design guide covers all major aspects of stack design and is supported by five appendices of technical reference material. The document will be reviewed every six months and updated on an as-needed basis to continually reflect the state-of-the-art in SOFC stack design.

  • Demonstrated that sodium volatility from soda lime glass and potassium volatility from potassium silicate had no discernible effect on performance of lanthanum strontium manganite/yttria-stabilized zirconia (LSM/YSZ) composite cathodes and lanthanum strontium cobalt ferite (LSCF) cathodes.

  • Identified new coal gas contaminant absorber materials. It was found that an absorber bed containing potassium carbonate completely captures phosphorus at temperatures of 350 degrees Celsius (ºC) and above, and completely captures arsenic at temperatures of 600 ºC and above. This represents a possible inexpensive option for removing these contaminants from coal gas.

  • Investigated the role of cell voltage on contaminant attack. A parametric study of cell voltage and coal contaminants phosphorus, arsenic, sulfur, selenium, and hydrogen chloride on anode degradation was completed. No changes in the cell degradation rate at different operating voltages were observed in the presence of phosphorus, arsenic, and hydrogen chloride; however, distinctly different responses to sulfur and selenium were observed at different voltages.

  • Transferred stack test fixture capability to NETL. Single-cell stack fixtures were delivered to and commissioned at NETL. This establishes the capability at NETL for independent parallel evaluation of materials and concepts for cells and stacks.

  • Devitrifying &"refractory” sealing glasses were optimized in terms of softening temperature, wetting behavior, and coefficient of thermal expansion.

  • Evaluated a new sealing approach incorporating a glass which is compliant at SOFC operating temperatures through single and dual atmosphere testing. Compliant seals improve mechanical robustness of SOFC stacks by reducing residual stresses during stack operation and thermal cycling. Process optimization studies were performed to control pore size and volume fraction porosity. Additions of zirconia fillers to form a glass/zirconia composite can improve dimensional stability at operating temperature. Collaborative development efforts at PNNL and ORNL involving glass only and glass/zirconia particle or fiber composites were continued.

  • Continued a long-term (>20,000 hours) study evaluating the effects of applying surface modifications to ferritic stainless steel interconnect materials prior to application of protective spinel coatings. Substantial improvement in scale adhesion and spallation resistance (compared to unmodified surfaces) can be achieved, particularly through surface blasting or grinding.

  • Provided topical report to SECA industry teams summarizing benefits of select surface modifications on scale adhesion / spallation resistance of steel-based interconnects.

  • Effects of humidity in air on LSM- and LSCF-based cathodes were quantified as a function of operating temperature and time.

  • Performed high temp XRD analyses on working LSCF cathodes as a function of operating time, voltage, and temperature. Changes in the perovskite structure and overall phase assemblage were quantified.

  • Developed and implemented a continuum damage-healing modeling framework to simulate the thermal-viscoelastic behavior of compliant glass seals in SOFC stacks using finite element analysis. Sensitivity studies on the seal design parameters were performed to evaluate the effects of material properties and operating conditions on seal mechanical behavior for the seal design engineering effort.

  • Developed a modeling framework that automatically creates reduced order models (ROMs) for SOFC stacks. The frame-work interface guides the user through the analysis procedure, samples and interrogates the multi-parameter operating space using the detailed stack model, performs regression to generate the response surfaces, and implements the response surfaces into a ROM submodel for general use within system modeling software.

  • Developed a user-friendly interface for the 2D SOFC-MP software to perform pre-processing and post-processing for SOFC stack evaluations. The pre-processing capability enables users to enter and modify SOFC model geometry, stack operating conditions, and simulation control parameters, while the post-processing capability helps users to visualize the solution results for various physical quantities across the stack model domain.

  • Benchmarked the 2D SOFC-MP modeling tool against experimental data. Model simulations for ten cases with different fuel compositions and temperature boundary conditions were successfully verified with experimental thermocouple data from a state-of-the-art stack for H2 and reforming fuel compositions.

  • Developed models to investigate humidity effects on cathode performance. Micro-scale modeling is used to understand competition of water with LSM activity and kinetics of possible reactions, while meso-scale modeling is used to quantify the corresponding electrochemical degradation within the electrode microstructure.

  • Modified the interconnect lifetime prediction methdology to be informed from interfacial indentation data of oxide scale-substrate interfaces with different surface modifications.

  • Completed a 24,000 hour oxidation test of several interconnect samples confirming that a shot-peening surface treatment can substantially extend interconnect lifetimes.


Project Details