Solid oxide fuel cell deposition

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

Zhitomirsky I and Petrie A. Electrophoretic deposition of electrolyte materials for solid oxide fuel cells. J. Mater. Sci. 2004 39 825-831. 

Ishihara T, Sato K, and Takita Y. Electrophoretic deposition of Y203-stabilized Zr02 electrolyte films in solid oxide fuel cells. J. Am. Ceram. Soc. 1996 79 913-919. 

Henne R. Solid oxide fuel cells a challenge for plasma deposition processes. J. Therm. Spray Tech. 2007 16 381-403. 

Schiller G, Henne R, Lang M, and Muller M. Development of solid oxide fuel cells (SOFC) for stationary and mobile applications by applying plasma deposition processes. Mat. Sci. Forum 2003 3 2539-2544. 

Xie Y, Neagu R, Hsu CS, Zhang X, and Deces-Petit C. Spray pyrolysis deposition of electrolyte and anode for metal-supported solid oxide fuel cell. J. Electrochem. Soc. 2008 155 B407-B410. 

Pederson LR, Singh P, and Zhou XD. Application of vacuum deposition methods to solid oxide fuel cells. Vacuum 2006 80 1066-1083. 

Yang D, Zhang X, Nikumb S, Deces-Petit C, Hui R, Marie R et al. Low temperature solid oxide fuel cells with pulsed laser deposited bi-layer electrolyte. J. Power Sources 2007 164 182-188. 

Labrincha JA, Li-Jian M, dos Santos MP, Marques FMB, and Frade JR. Evaluation of deposition techniques of cathode materials for solid oxide fuel cells. Mater Res. Bull. 1993 28 101-109. 

In general, reforming of the CH4 fuel with excess H2O outside the cell has been practiced both in molten carbonate and solid oxide fuel cell systems in order to produce H2, more reactive on a fuel cell anode, and to avoid the possible deposition of C. This reforming reaction... 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

Gupta G.K., Dean A.M., Hecht E.S., Zhu H., Kee R.J. (2005) The influence of heterogeneous chemistry and electrochemistry on gas-phase moleculear-weight growth and deposit formation. In Solid Oxide Fuel Cells IX (SOFC-IX), Electrochemical Society Proceedings, Quebec PQ, 15-20 May, Vol. 1, Cells, Stacks, and Systems, S.C. Singhal and J. Mizusaki (Eds.), The Electrochemical Society, Pennington, NJ, pp. 679-688. 

K.L. Choy, W. Bai, and B.C.H. Steele, New Deposition Process for Dense YSZ Lilms onto Porous Electrodes, Solid Oxide Fuel Cells, Vol.97-40, 1997, pp.177-182. 

PEVD has been applied to deposit auxiliary phases (Na COj, NaNOj and Na SO ) for solid potenfiometric gaseous oxide (CO, NO, and SO ) sensors, as well as a yttria stabilized zirconia (YSZ) ceramic phase to form composite anodes for solid oxide fuel cells. In both cases, the theoretically ideal interfacial microstructures were realized. The performances of these solid state ionic devices improved significantly. Eurthermore, in order to set the foundation for future PEVD applications, a well-defined PEVD system has been studied both thermodynamically and kinetically, indicating that PEVD shows promise for a wide range of technological applications. 

The present availabihty of numerous types of solid electrolytes permits transport control of various kinds of mobile ionic species through those solid electrolytes in solid electrochemical cells, and permits electrochemical reactions to be carried out with the surrounding vapor phase to form products of interest. This interfacing of modem vapor deposition technology and solid state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). PEVD has been applied to fabricate two types of solid state ionic devices, i.e., solid state potenfiometric sensors and solid oxide fuel cells. Investigations show that PEVD is the most suitable technique to improve the solid electrolyte/electrode contact and subsequently, the performance of these solid state ionic devices. 

Pale yellow cerium dioxide (ceria, ceric oxide) has the fluorite structure and is used in catalysis" ", solid oxide fuel cells (SOFC)", thin film optical waveguides" , reversible oxygen storage materials for automobile catalysts" and for doping copper oxide superconductors". The diverse cerium enolate precursors and deposition methods used in the formation of cerium oxide thin films are summarized in Table 6, whereby the most common precursor for ceria is Ce(thd)4. 

Figure 3.29. Scanning electron microscope picture of the electrode-electrolyte structure along a perpendicular cut. Top screen-printed Lao.jSro 4CO0 FeogOj positive electrode. Middle spray-deposited electrolyte, YSZ = 8 mol% YjOg stabilised ZrOj. Bottom negative electrode, NiO and YSZ in ratio 7 3, in cermet CeOj. (From D. Perednis and L. Gauckler (2004). Solid oxide fuel cells with electrolytes prepared via spray pyrolysis. Solid State Ionics 166,229-239. Reprinted by permission from Elsevier.)...

Another Ni-based solid oxide fuel cell (SOFC) electrode was developed on which a YSZ (yttria-stabilized zirconia) cermet and Lanthanum chromite were deposited by a slurry coating method. It was also suggested that a plasma spraying process can be used for the cermet deposition on the electrodes. The following reactions are expected to take place in a fuel cell employing a natural gas source, where internal reforming takes place on the Ni-YSZ electrode ... 

Since these first reports, Iwahara and other investigators have studied the conductivities (both ionic and electronic), conduction mechanism, deuterium isotope effect, and thermodynamic stability of these materials. The motivation for most of this work derives from the desire to utilize these materials for high temperature, hydrogen-fiieled solid oxide fuel cells. In a reverse operation mode, if metal or metal oxide electrodes are deposited onto a dense pellet of this material and heated to temperature T, the application of an electric potential to the electrodes will cause a hydrogen partial pressure difference across the pellet according to the Nemst equation ... 

Liu, Y., S.W. Zha, and M.L. Liu, Novel nanostructured electrodes for solid oxide fuel cells fabricated by combustion chemical vapor deposition (CVD). Advanced Materials, 2004, 16(3) p. 256-260... 

Key words Combustion Chemical Vapor Deposition/Thin Film Electrol rte/Solid Oxide Fuel Cells... 

Key words Solid Oxide Fuel Cells/Electron Beam Deposition/Porosity/Zirconia Ceramics... 

Decreasing operation temperature of solid oxide fuel cells (SOFCs) and electrocatalytic reactors down to 800-1100 K requires developments of novel materials for electrodes and catalytic layers, applied onto the surface of solid electrolyte or mixed conducting membranes, with a high performance at reduced temperatures. Highly-dispersed active oxide powders can be prepared and deposited using various techniques, such as spray pyrolysis, sol-gel method, co-precipitation, electron beam deposition etc. However, most of these methods are relatively expensive or based on the use of complex equipment. This makes it necessary to search for alternative synthesis and porous-layer processing routes, enabling to decrease the costs of electrochemical cells. Recently, one synthesis technique based on the use... 

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