Exploration of Electrophoretic Deposition of YSZ Electrolyte for Solid Oxide Fuel Cells
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EXPLORATION OF ELECTROPHORETIC DEPOSITION OF YSZ ELECTROLYTE FOR SOLID OXIDE FUEL CELLS Zhigang Xu, Gukan Rajaram, Jag Sankar Center for Advanced Materials and Smart Structures North Carolina Agricultural and Technical State University 1601 East Market Street Greensboro, NC 27411, U.S.A. ABSTRACT The suspensions of yttria stabilized zirconia (YSZ) were prepared in pure acetylacetone and ethanol and their mixtures. In all of the suspensions, YSZ thin films were obtained using electrophoretic deposition technique on the substrates of stainless steel and porous strontiumdoped lanthanum manganite (LSM) which is a typical cathode materials used in solid oxide fuel cells (SOFCs). The deposition behavior in the different suspensions was studied. The deposited films were dried at room temperature and then sintered at high temperature. Observation with scanning electron microscopy (SEM) showed the sintered YSZ were of high density. INTRODUCTION Electrophoretic deposition (EPD) is a process in which the charged particles in an appropriate solvent move under the influence of the direct electric field towards an oppositely charged electrode and coagulate thereon to form a stable deposit. In the past research and applications, it was used to prepare ceramic laminates [1, 2], components in electrochemical cells [3], and ceramic superconductors [4], etc. It was recently introduced to the area of the manufacturing SOFCs, since thin film electrolytes are highly desired for the fuel cells to work at reduced temperatures and higher efficiencies. This deposition technique is especially attractive for SOFC application owing to simple, low cost equipment and ease of deposition of films of controlled thickness on substrates with even complex shape. The important issues in preparation of a suspension suitable for deposition are to choose appropriate solvent and charging methods. Suspensions with organic solvents are preferred over aqueous suspensions for depositions of high-performance ceramics, since EPD in aqueous solvents is accompanied with significant gas evolution (hydrogen on cathode and oxygen on anode) and results in porous deposits. Ceramic particles must be charged in order to generate EPD effect. There are usually two charging mechanisms, i.e., electrostatic charging and electrosteric charging. Electrostatic charging is realized by the adsorption of common ions on the surface of the particles to form electrical double layers. The same charges on the two approaching particle create repulsion to oppose the attraction from van der Waals interactions. Electrosteric charging was generated by adsorption of polyelectrolyte on the surface of the particles. EPD is a low-cost and efficient method to process electrolyte coatings on porous electrodes of fuel cells. The research in our center includes two aspects, one of which is to make porous cathode and anode substrates using slurry casting, the other of which is to coat the substrates with YSZ electrolyte by electrophoretic deposition. By studying of the various combinations of
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