Papers

ICMCTF2005 Session A2: Coatings for Use in Fuel Cells, Catalysis and Membranes

Thursday, May 5, 2005 8:30 AM in Room Sunrise

Thursday Morning

Start	Invited?	Item
8:30 AM		A2-1 Coatings and Deposition Processes for Solid Oxide Fuel Cells (SOFC): a Review P. Singh, L. Pederson (Pacific Northwest National Laboratory) Ceramic and metallic coatings and deposition processes, currently being investigated for the fabrication and processing of solid oxide fuel cell components, will be reviewed. Processes such as thermal plasma and filtered arc plasma, chemical and electrochemical vapor deposition (CVD & EVD), physical and electron beam physical vapor deposition (PVD & EBPVD) will be examined and discussed for the fabrication of dense oxygen ion conducting electrolyte (YSZ) and electronically conducting chromite interconnection. Corrosion resistant coatings for interconnects and seals will also be examined. Materials composition and structure will be discussed.
9:10 AM		A2-3 A Comparison of Electrical Properties of Sputter-Deposited Electrolyte Coatings Dedicated to Intermediate Temperature Solid Oxide Fuel Cells P. Briois (Laboratoire de Science et Génie des Surfaces, France); A. Billard (Ecole des Mines-Parc de Saurupt, France) Solid oxide fuel cells are of increasing interest for future environmental friendly energy generation. The major problem related to actual devices is the rather high temperature required, of about 1000°C, yielding a poor ageing behaviour due to the reactivity of the cell core components. The tendency to avoid these ageing phenomena tends to decrease the operating temperature of SOFC to an intermediate temperature domain of 600-700°C, which however raises the problem of insufficient ionic conductivity of O^2- of actual electrolytes. Among the solutions involved to overcome this drawback, the synthesis of about 5-10 µm thick electrolyte coatings is expected to decrease the resistance at a convenient level. In this paper, we present recent results of a study concerning the synthesis of 1-5 µm thick Yttria Stabilised Zirconia (YSZ), Gadolinium-Doped Ceria (GDC) and La_2-xY_xMo₂O₉ (LaMOx) sputter-deposited coatings from metallic targets in various Ar-O₂ reactive mixtures. In a first part, we describe the experimental vessel equipped with an original Optical Transmission Interferometry (OTI) device developed at the laboratory for in situ control of the synthesised films. The second part is ascribed to their chemical, microstructural and structural characterisation in relation with the deposition conditions. Finally, the ionic transport characteristics of the films are investigated via impedance spectroscopy measurements performed at various temperatures up to 800°C.
9:30 AM		A2-4 Processing of Yttria-Stabilized Zirconia (YSZ) Thin Films on Dense and Porous Substrates Y. Pan, J.H. Zhu (Tennessee Technological University); M.Z. Hu (Oak Ridge National Laboratory); E.A. Payzant (Oak Rudge National Laboratory) In anode-supported solid oxide fuel cells (SOFCs), thin films based on yttria-stabilized zirconia (YSZ) are widely used as the electrolyte material. In this study, YSZ thin films with Zr:Y = 0.84:0.16 in molar ratio, were coated on dense Si substrates and porous Ni-YSZ anodes using the spin coating technique. Two approaches were used to synthesize the YSZ films. The first one utilized a commercial precursor, YSZ-0007 polymer (from Chemat Company) diluted with certain solvent. By controlling the content of the solvent in the solution, dense, crack-free YSZ films of 500 nm were obtained on dense Si substrate, after 8 coating runs with a final annealing of 700°Cx4h. Systematic X-ray diffraction study indicated that the YSZ films started to crystallize at 350-400°C, and at temperature ≥ 600°C, the YSZ films were fully crystalline with cubic structure. In the second approach, a new YSZ precursor was prepared, and improved YSZ film quality was achieved by controlling the viscosity of the solution. Based on the success of these two approaches on dense Si substrates, YSZ films on porous Ni-YSZ substrate were processed, and the problems and promises of such films as thin-film SOFC electrolyte were assessed and discussed.
9:50 AM		A2-6 High Temperature Oxidation, Cr Volatility and Surface Electrical Conductivity of Ferritic Steel with and without Filtered Arc Cr-Al-O-N and/or Filtered Arc-Assisted E-Beam Co-Mn-O Coatings V.I. Gorokovsky (Arcomac Surface Engineering, LLC); P.E. Gannon, M.C. Deibert, R.J. Smith, K. Asghar, M. Kopczyk (Montana State University); D. Van Vorous (Arcomac Surface Engineering, LLC); Z.G. Yang (Pacific Northwest National Laboratory); J.W. Stevenson (Pacific Northwest Natinal Laboratory); S. Visco, C. Jacobson, H. Kurokawa (Lawerence Berkley National Laboratory); S. Sophie (NASA Glenn Research Center) Reduced operating temperatures (600-800°C) of Solid Oxide Fuel Cells (SOFCs) may enable the use of inexpensive ferritic steels as interconnects. Due to the demanding SOFC interconnect operating environment, protective coatings are gaining attention to increase long-term stability. In this study, filtered arc and filtered arc-assisted e-beam coatings¹ from the Co-Mn-Cr-Al-O-N elemental system were deposited on ferritic steel and subsequently annealed in air for various time intervals. Surface oxidation was investigated using RBS, SEM and EDS analyses. Cr-volatilization was evaluated using a transpiration apparatus and ICP-MS analysis of the resultant condensate. Electrical conductivity (Area Specific Resistance) was studied as a function of time using the four-point technique with Ag as electrode. The oxidation behavior, Cr volatilization rate, and electrical conductivity of the coated and uncoated samples are reported. Transport mechanisms for various oxidizing species and coating diffusion barrier properties are discussed. @super 1!V.I. Gorokhovsky, R. Bhattacharya, and D. G. Bhat: Surface Coatings and Technology, 2001, vol. 140, pp. 82-92.
10:10 AM		A2-7 Influence of Post Treatments on the Contact Resistance of Plasma Sprayed La_{0.8√sub 0.2}MnO₃ Coating on SOFC Metallic Interconnector D.P. Lim, D.S. Lim (Korea University, South Korea); J.S. Oh, I.W. Lyo (Research & Development Division for Hyundai Motor, South Korea) A decrease in cell operation temperature to the intermediate temperature range of 600-700°C allows the use of cheaper and more conductive metallic interconnect materials instead of ceramics. Stainless steel considered as one of candidate material owing to its adaptable thermal expansion coefficient and low price. However, life time performance is restricted owing to insulating oxide scale on the steel surface and degradation of cathode performance due to vaporization of chromia-containing oxide scale. In order to reduce degradation of cell performance, an effective protective layer should be developed. In this study, LSM(La_{0.8√sub 0.2}MnO₃) coating was attempted by plasma spraying method. Solid state reaction method was introduced to synthesize LSM powders prior to plasma spraying. Microstructure and contact resistance with respect to temperature and oxidation time were evaluated. Uniform and dense coatings were achieved to improve the long-term oxidation behavior and contact resistance. Post surface treatment with plasma and thermal annealing were proposed to improve the performance of plasma spray coated metallic interconnector. The results sowed that post treatments lowered the high temperature contact resistance efficiently. The variation of the porosity, degree of crystallinity and other properties of the plasma sprayed LSM coating after post treatment were investigated to explain the improved high temperature conductivity behavior. Research supported by Research & Development Division for Hyundai Motor Company & Kia Motors Corporation.
10:30 AM		A2-8 Fabrication of of Self-Supported Pd-Alloy Membranes using Vacuum Deposition Methods B.R. Lanning, C.A. Engel, W.J. Riggs (Southwest Research Institute); E. Arslan (Ataturk University, Turkey); J.D. Way, O. Ishteiwy (Colorado School of Mines) Noble metal alloy membranes are a key enabling technology in the development of fuel processors for fuel cells and as purifiers for coal gasification. One of the impediments to their broad application and use is the cost of palladium, the critical element that allows efficient diffusion and purification of hydrogen in the fuel stream. In addition, reductions in membrane thickness and increases in size are needed to further improve purification efficiency and reduce part count. To address these issues, we have investigated the use of large-area vacuum deposition methods to fabricate dense, freestanding Pd-alloy membranes up an order of magnitude thinner than the current state of the art of approximately 25 microns with areas up to 20 in2 . A key element of our approach has been to deposit the membranes onto flexible, removable supports that can be recycled after use. Details of the fabrication process and hydrogen purification performance of these membranes will be presented.
10:50 AM		A2-9 Protonic Conductivity Nanostructured Ceramic Film with Improved Resistance to Carbon Dioxide at Elevated Temperatures X.Q. Ma, J.X. Dai, H. Zhang, D. Reisner (US Nanocorp, Inc.) Hydrogen is a high value product, referring to the fact that it is a clean fuel with low emission, and thereby alleviates the real threat of "Greenhouse effect." From the "hydrogen economy" point of view, the predominant way of producing hydrogen is from fossil sources or natural gas. A dense ceramic protonic conductivity film can be used to separate hydrogen from reformed fuel or syngas in gasification process at high temperatures. However, existing ceramic films are proven to severely degrade in CO₂-containing environments. In this work, a co-doped BaCeO₃ material was proposed for higher protonic conductivity and better chemical stability. Nanostructured BaCeO₃-based film was fabricated from nano-grain feedstock in air plasma spray method. The protonic film has demonstrated superior properties to existing ceramic protonic films for hydrogen separation in terms of chemical stability, protonic and electronic conductivity and thermo-mechanical properties in the range of 600-800°C. This work will demonstrate a methodology for significantly improving chemical stability, solid ionic conductivity, together with acceptable mechanical properties for a protonic membrane system, by using a doping material technique and incorporating a nanostructured membrane concept into the manufacturing process.