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Title: Evaluation of a surface treatment on the performance of Crofer 22 APU in a SOFC Button Cell

Abstract

Crofer 22 APU is a 22 weight percent Cr ferritic stainless steel developed at Forschugszentrum Jülich and manufactured by ThysennKrupp for application as an interconnect in SOFC. We have developed a cerium oxide surface treatment which greatly enhances the oxidation resistance of this and many other alloys. Minimizing scale growth is helpful for improving the performance in interconnect application; however, the overall performance is dependant upon such things as scale thickness, scale resistivity, etc. We report on the in-cell performance of cerium treated and conventional Crofer 22 APU and discuss the results in terms of the microstructure and scales that form.

Authors:
; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, and Morgantown, WV
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
912942
Report Number(s):
DOE/NETL-IR-2007-076
TRN: US200802%%473
DOE Contract Number:
None cited
Resource Type:
Conference
Resource Relation:
Conference: 2007 TMS Annual Meeting: Symposium on Materials in Clean Energy Systems II, Orlando, FL, Feb. 25-Mar. 1, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALLOYS; CERIUM; CERIUM OXIDES; ENERGY SYSTEMS; EVALUATION; MICROSTRUCTURE; OXIDATION; PERFORMANCE; SOLID OXIDE FUEL CELLS; STAINLESS STEELS; SURFACE TREATMENTS; THICKNESS; ferritic stainless steel; interconnect; SOFC; solid oxide fuel cell; cerium oxide; surface treatment; oxidation resistance; Crofer 22 APU

Citation Formats

Alman, D.E., Johnson, C.D., and Jablonski, P.D. Evaluation of a surface treatment on the performance of Crofer 22 APU in a SOFC Button Cell. United States: N. p., 2007. Web.
Alman, D.E., Johnson, C.D., & Jablonski, P.D. Evaluation of a surface treatment on the performance of Crofer 22 APU in a SOFC Button Cell. United States.
Alman, D.E., Johnson, C.D., and Jablonski, P.D. Thu . "Evaluation of a surface treatment on the performance of Crofer 22 APU in a SOFC Button Cell". United States. doi:.
@article{osti_912942,
title = {Evaluation of a surface treatment on the performance of Crofer 22 APU in a SOFC Button Cell},
author = {Alman, D.E. and Johnson, C.D. and Jablonski, P.D.},
abstractNote = {Crofer 22 APU is a 22 weight percent Cr ferritic stainless steel developed at Forschugszentrum Jülich and manufactured by ThysennKrupp for application as an interconnect in SOFC. We have developed a cerium oxide surface treatment which greatly enhances the oxidation resistance of this and many other alloys. Minimizing scale growth is helpful for improving the performance in interconnect application; however, the overall performance is dependant upon such things as scale thickness, scale resistivity, etc. We report on the in-cell performance of cerium treated and conventional Crofer 22 APU and discuss the results in terms of the microstructure and scales that form.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}

Conference:
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  • Pack cementation-like Cerium based surface treatments have been found to be effective in enhancing the oxidation resistance of ferritic steels (Crofer 22APU) for solid oxide fuel cell (SOFC) applications. The application of either a CeN- or CeO2 based surface treatment results in a decrease in weight gain by a factor of three after 4000 hours exposure to air+3%H2O at 800oC. Similar oxide scales formed on treated and untreated surfaces, with a continuous Cr-Mn outer oxide layer and a continuous inner Cr2O3 layer formed on the surface. However, the thickness of the scales, and the amount of internal oxidation were significantlymore » reduced with the treatment, leading to the decrease in oxidation rate. This presentation will detail the influence of the treatment on the electrical properties of the interconnect. Half-cell experiments (LSM cathode sandwiched between two steel interconnects) and full SOFC button cell experiments were run with treated and untreated interconnects. Preliminary results indicate the Ce treatment can improve SOFC performance.« less
  • Significant progress in reducing the operating temperature of SOFCs below 800oC may allow the use of chromia-forming metallic interconnects at a substantial cost savings. Hydrogen is the main fuel for all types of fuel cells except direct methanol fuel cells. Hydrogen can be generated from fossil fuels, including coal, natural gas, diesel, gasoline, other hydrocarbons, and oxygenates (e.g., methanol, ethanol, butanol, etc.). Carbon oxides present in the hydrogen fuel can cause significant performance problems due to carbon formation (coking). Also, literature data indicate that in CO/CO2 gaseous environments, metallic materials that gain their corrosion resistance due to formation of Cr2O3,more » could form stable chromium carbides. The chromium carbide formation causes depletion of chromium in these alloys. If the carbides oxidize, they form non-protective scales. Considering a potential detrimental effect of carbon oxides on iron- and nickel-base alloy stability, determining corrosion performance of metallic interconnect candidates in carbon oxide-containing environments at SOFC operating temperatures is a must. In this research, the corrosion behavior of Crofer 22 APU and Haynes 230 was studied in a CO-rich atmosphere at 750°C. Chemical composition of the gaseous environment at the outlet was determined using gas chromatography (GC). After 800 h of exposure to the gaseous environment the surfaces of the corroded samples were studied by scanning electron microscopy (SEM) equipped with microanalytical capabilities. X-ray diffraction (XRD) analysis was also used in this study.« less
  • Creep deformation becomes relevant for a material when the operating temperature is near or exceeds half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 1073oK. High temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and CTE compatibility with other SOFC components. Since the melting temperature of most stainless steel is around 1800oK, possible creep deformation of IC under the typical cell operating temperature should not be neglected. In this paper, themore » effects of interconnect creep behavior on stack geometry change and stress redistribution of different cell components are predicted and summarized. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the fuel and air channel geometry changes due to creep of the ferritic stainless steel interconnect, therefore indicating possible SOFC performance change under long term operations. IC creep models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the deformed configuration of the SOFC stack under the long term steady state operating temperature. It is found that creep behavior of the ferritic stainless steel IC contributes to narrowing of both the fuel and the air flow channels. In addition, stress re-distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.« less
  • This model is based on a closed-form calculation of SOFC voltage for a given current, fuel and air composition, and temperature. The response characteristics are adjustable to changes in stack component materials and dimensions as well as to electrode porosity. The model performs a ?unit-cell? calculation in the sense that it calculates performance at steady state, assuming that fuel composition, air composition and temperature are homogeneous over the active area. The usual overpotential terms account for ohmic resistance of the cell components, loss due to charge transfer at the electrodes, and losses due to diffusion of reactants into and productsmore » out of the porous electrodes. Although the form of the algorithm is based on theoretical treatments of the overpotential terms, several adjustable parameters are used to calibrate the model to closely match actual small-scale single-cell data that was taken over a range of temperatures and fuel compositions (see Simner et al, ?Development of Cathode Materials and Fabrication Techniques for Low Temperature SOFCs? elsewhere in these proceedings). The calibrated performance model algorithm is used to calculate electrochemical activity of each computational cell within a comprehensive electrochemical model of the stack (see Recknagle et al, ?Thermo-Fluid-Electrochemical Modeling of Planar SOFC Stacks in Three-Dimensions? elsewhere in these proceedings). This poster discusses unit cell performance using I-V curves predicted for a variety of chemical conditions and cell materials configurations.« less
  • Two 22-cells 19Ah Nickel-Hydrogen (Ni-H2) Single Pressure Vessel (SPV) Qual batteries, one each from EPI/Joplin and EPI/Butler, were designed and procured. The two batteries differ in the cell encapsulation technology, stack preload, and activation procedure. Both the Butler and Joplin batteries met the specified requirements when subjected to qualification testing and completed 2100 and 1300 LEO cycles respectively, with nominal performance. This paper discusses advantages, design features, testing procedures, and results of the two single pressure vessel Ni-H2 batteries.