Viscoelastic Inks for Direct-Write Microfabrication of Single-Chamber Micro Solid Oxide Fuel Cells With Coplanar Thick E
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Viscoelastic Inks for Direct-Write Microfabrication of Single-Chamber Micro Solid Oxide Fuel Cells With Coplanar Thick Electrodes Melanie Kuhn1, Ranjeet B. Rao2,* and Daniel Therriault1 1
Department of Mechanical Engineering, École Polytechnique de Montréal, Montreal, QC, H3T 1J4, Canada. 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, U.S.A. *Current address: Xerox PARC, Palo Alto, CA, 94304, U.S.A. ABSTRACT Single-chamber micro solid oxide fuel cells (SC-µSOFCs) with coplanar electrodes were fabricated using a robotically controlled direct-write microfabrication approach. Viscoelastic, gel-based inks were employed to create homogeneous electrodes of controlled width and interelectrode distance as well as uniform cross-sectional thickness. Electrode powders, NiOYSZ (yttria-stabilized zirconia) for the anode and (La0.8Sr0.2)0.98MnO3-YSZ for the cathode, were first dispersed with a cationic polyethyleneimine solution. Polyacrylic acid was added to induce a fluid-to-gel transition. The rheology of the fabricated inks was characterized. The inks were then extruded through cylindrical micronozzles and deposited onto YSZ electrolyte substrates using a robotic deposition apparatus. Thickness and width of the sintered electrodes were close to the diameter of the extrusion nozzle. The improved shape retention of the deposited electrodes also enabled the fabrication of continuous electrodes with square cross-section. The cathode adhered very well to the electrolyte during sintering. However, the mismatch between the thermal expansion coefficient of anode and electrolyte seems to cause detaching and breaking of the anode so that electrochemical characterization of the fabricated cells was not yet possible. INTRODUCTION Single-chamber solid oxide fuel cells (SC-SOFCs) are operated in mixtures of fuel and oxidant gas, which simplifies fuel cell design and eliminates high-temperature gas-tight sealing issues of conventional dual-chamber SOFCs. The working principle of these fuel cells is based on the selectivity of the electrodes for the respective reactions, that is, fuel oxidation at the anode and reduction of the oxidant at the cathode [1]. The single-chamber approach enables novel cell designs such as the single-face configuration, where both anode and cathode are located on the same side of the electrolyte (e.g., single parallel electrode pairs or interdigitated electrodes) [2]. Closely-spaced (< 1 mm), small (width < 1 mm) electrodes were found to reduce ohmic resistance and yield higher cell performance [2,3]. Standard lithography-based microfabrication techniques have the resolution to fabricate microscale electrodes, but they do not permit to easily create structures of two different materials with porous microstructure on the same side of a substrate. Microfluidic lithography [4] and micromolding [5] were investigated for the fabrication of coplanar microscale electrodes. However, the versatility of these techniques is limited by the neces
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