Rebecca Green, Materials Science and Engineering
Title: Synthesis of Monodisperse Spinel Oxide Core-Shell Nanoparticles
Mentor: Professor Richard D. Robinson, Materials Science and Engineering
Funding from corporate partner, Phillips 66.
Spinel oxide nanoparticles (NPs) possess interesting electrochemical properties, making them auspicious candidates for alternative supercapacitor electrode materials. However, these materials often possess poor electrical conductivities, which can ultimately hamper supercapacitor rate capability and power density. To enhance the conductivity and overall electrochemical performance of these NPs, a core-shell architecture can be employed. Such a structure combines materials with complementary properties, such as the high conductivity of Fe3O4 and the high specific capacitances of MnFe2O4 and CoFe2O4 to improve system performance. However, the production of these NPs requires a readily replicable and adaptable synthesis technique. In this study we report on the synthesis of monodisperse Fe3O4 @ MnFe2O4 core – shell NPs using a heat-up method and seed-mediated growth. The process involves two separate syntheses to produce the cores and then the core-shell NPs, both syntheses involving metal acetylacetonates, 1,2-hexadecanediol, and oleic acid and oleylamine as ligands. We found that varying the relative amounts of shell precursors, core seeds, and ligand materials alters the resultant NP size and creates crystal facets. Furthermore, we also show that this technique can be extended to produce other spinel oxide core-shell systems, in which Fe3O4 and CoFe2O4 or MnFe2O4 can comprise either the core or shell material. Thus, we anticipate this synthesis will become a starting point for producing more sophisticated spinel oxide core-shell architectures.
The rise in renewable energy sources, including hydro-power, wind power, and solar energy, has increased the demand for efficient energy storage systems. Among the leading systems are lithium-ion batteries and supercapacitors. Supercapacitors have gained attention over batteries in recent years, offering faster charge and discharge rates, long cycle lives, and low environmental costs. However, although they may boast superior power densities, capacitors historically possess lower energy densities than Li-ion batteries. Therefore, recent research efforts aim to increase energy density in supercapacitors. More broadly, the important supercapacitor performance metrics are specific capacitance, energy density, power density, cycling stability, and rate capability, which is the variation of specific capacitance at different current densities. Supercapacitor electrode materials are typically comprised of carbon, conducting polymers, or transition metal oxides. Of the metal oxides, RuO2 produces the highest performing faradaic supercapacitors, but this material is both financially and environmentally costly. As alternative electrode materials, spinel oxide nanoparticles are of interest because they feature large surface areas, abundant electroactive sites, large demonstrated specific capacitance values, and low costs.
The results of this study may ultimately enhance supercapacitor performance, making energy storage more efficient. Efficient energy storage is the key to realizing the potential of renewable energy sources, as well as to enabling the emergence of new technology for society.