Flexible metal oxide nanowire electrolytes with metallic nanostructured platinum and nickel three phase boundaries for application in solid oxide fuel cells (SOFCS).

Abstract

Metal oxide electrolytes have been used extensively in applications such as solid oxide fuel cells due to their ability to permit oxide ion (O 2- ) conductance as a solid electrolyte at elevated temperatures. Yttrium oxide (Y 2 O 3 )-stabilized zirconium oxide (ZrO 2 ) (YSZ) and tungsten (VI) oxide (WO 3 )-stabilized bismuth oxide (Bi 2 O 3 ) (WBO) are among the most widely used materials for these applications. The goal of this dissertation is to synthesize a network of one dimensional ZrO2, YSZ, Bi 2 O 3 and WBO nanowires that are coated with elemental platinum (Pt 0 ) nanoparticles (as the cathode) and nanostructures of metallic nickel (Ni 0 ) (as the anode). Reduction in the size of the electrolyte, cathode, and anode materials increases the reactive surface area for the reduction and oxidation of oxygen and hydrogen respectively, thus ideally increasing the efficiency of the SOFC. In this research, the synthesis of nanostructured solid electrolytes was accomplished using either (a) suspended particle/electrospinning/annealing route or (b) a sol-gel method incombination with electrospinning and annealing. The metal oxide nanowire films maintained its flexibility post-annealing only when its thickness was within a range of 10?m to 15?m. The necessary three phase boundaries (TPB), where the reduction of oxygen and oxidation of hydrogen takes place in a catalytic fuel cell application, was prepared by thermal reduction of hexachloroplatinic acid (H 2 PtCl 6 ) and tris(2,2¿-bipyridine)nickel (II) chloride (Ni(2,2¿-bipyridine) 3 ]Cl 2. 5H 2 O) to elemental platinum and nickel nanocrystal form, respectively. The characterization of these materials was achieved primarily by Field Emission Scanning Electron Microscopy (FE-SEM) (JEOL JSM-7100F), Transmission Electron Microscopy (TEM) (JEOL JEM-2100), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD). Temperature dependent ionic conductivity measurements were performed to investigate the current carrier mobility and activation energy associated with the solid electrolyte under nitrogen and oxygen atmospheres, separately. The data obtained from these investigations was used to evaluate the conductivity of the electrolyte under various conditions in order to construct a nano-sized SOFC.