Electric double layer capacitors, or supercapacitors, have high theoretical capacities and faster charge/discharge rates than Li-ion batteries. Because they store charge via electrostatic interactions between the electrode surface and ions in the electrolyte, increased specific surface area of electrode materials will increase the theoretical storage capacity of next-generation devices. Nanofiber-based electrodes have fewer issues with agglomeration and better long-term stability than nanoparticle-based electrodes, while maintaining extremely high surface area to volume ratios. As a potential electrode material, Mn2O3 is low-cost, naturally abundant, and environmentally benign. Electrospinning with subsequent thermal decomposition is a facile fabrication method for creating Mn2O3 nanofibers. Composite fibers consisting of a coordination polymer, polyvinylpyrrolidone, and oxide precursor, manganese acetate tetrahydrate, are electrospun. Calcination is used to burn out the polymer matrix and convert the salt to manganese oxide while retaining the high aspect ratio fiber morphology.
Although Mn2O3 nanofibers have been prepared by thermal decomposition of a coordinating polymer-oxide precursor composite fiber, the influence of calcination conditions on specific surface area have not been well-explored. The proposed work will examine the effects of calcination time, temperature, and environmental composition on fiber surface areas and corresponding electrochemical capacitance as compared to nanoparticle-based electrodes. Thermal analysis will be performed with thermogravimetry and differential scanning calorimetry to determine glass transition and decomposition temperatures of the as-spun composite fibers. The post-calcination fibers will be examined with X-ray diffraction to confirm phase and obtain information on crystallite size. Scanning electron microscopy will be used for morphological examination and qualitative examination of porosity resulting from changes in calcination parameters. To quantify changes in specific surface area, the Brunauer-Emmett-Teller (BET) method will be used on calcined fibers and compared to values measured for nanoparticles prepared from the oxide precursor. Increased surface area detected by BET may not necessarily be accessible to ions in the electrolyte, so to evaluate the accessible surface area, the fibers and particles will be processed into working electrodes. Electrochemical analysis including cyclic voltammetry and linear voltammetry will be utilized to assess the accessible surface area of fiber-based vs. particle-based electrodes based on measured capacitance. Preliminary results have shown that modifications to the gas composition and calcination time result in varied porosity, surface features, and cross-sectional morphologies. An understanding of the relationship between processing conditions and fiber morphology will allow for tunability of enhanced surface area, electrochemical capacitance, and supercapacitor performance.
5:00 PM–7:00 PM Apr 23, 2019 (US - Arizona)
PCC North, 300 Level, Exhibit Hall C-E