Inorganic Electrospun Nanofibers: From Rational Catalyst Design To Power Generation Materials

摘要

Purely inorganic electrospun nanofibers containing iron and nickel catalytic nanocrystals are generated via sol-gel chemistry, with those nanocrystals in various concenctrations as well as locations by coaxial electrospinning. These nanofibers, following thermal treatment and precursor crystallization, are then applied as catalysts to the alkaline hydrolysis of glucose where they display conversions that increase with increasing catalyst concentration at the surface of the nanofiber. However, a long pretreatment drying time is required to reactivate the entrained catalyst. To decrease the pretreatment drying time a new fabrication method is developed; binding high concentrations of metal salts to a water-soluble polymer, electrospinning and using thermal treatments to remove the polymer and crystallize the metal salts. Nanofibers of a variety of morphologies and concentrations are fabricated through this approach and applied to the alkaline hydrolysis of glucose. These results detail that by increasing the concentration of available catalytic surface area within the diffusion length scale of the reactant, the temperature range at which near pure hydrogen is produced increases nearly 60˚C. Subsequently this highly loaded water based electrospinning approach is used to generate nanofibers for a variety of applications. The electrical conductivity of these nanofibers are found for a variety of metals, including copper, iron, nickel and cobalt, and shown to be: tunable with the crystal morphology within the nanofiber matrix, orders of magnitude higher than conductivities reported for other one dimensional materials, and directionally controlled by the anisotropy of the nanofiber mat. The magnetic properties of iron, nickel, and cobalt nanofibers are shown to be a function of both size and temperature ranging from near superparamagnetic behavior to highly coercive as controlled by precursor inclusion and thermal treatment procedure. Alternating layers of aligned nanofibers are subsequently used to overcome curling effects caused by volume loss during thermal treatment. By orienting perpendicular layers next to each other, axial shrinkage is minimized thereby maintaining long, linear nanofibers as well as flat, macroscopic mats. Finally, using the highly loaded water-based technique and the alternating layers of nanofibers, preliminary nanofibrous materials are synthesized for power generation applications such as lithium ion battery anodic materials and thin film photovoltaic devices. These materials display great promise due to high surface areas containing proper band gap or high capacity materials, but many future works are proposed for these materials.