School of Natural Sciences and Mathematics

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Browsing School of Natural Sciences and Mathematics by Author "0000 0000 4239 3958 (Chabal, YJ)"

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    Novel Binder-Free Electrode Materials for Supercapacitors Utilizing High Surface Area Carbon Nanofibers Derived from Immiscible Polymer Blends of PBI/6FDA-DAM:DABA
    (Royal Society of Chemistry, 2018-06-01) Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.; 0000 0000 4239 3958 (Chabal, YJ); 0000-0002-3225-0093 (Ferraris, JP); Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.
    Carbon nanofibers with high surface area have become promising electrode materials for supercapacitors because of their importance in increasing energy density. In this study, a high free volume polymer, 6FDA-DAM:DABA (6FDD) was blended with polybenzimidazole (PBI) in different ratios to obtain different compositions of PBI/6FDD immiscible polymer blends. Freestanding nanofiber mats were obtained via electrospinning using blend precursors dissolved in N,N-dimethylacetamide (DMAc). Subsequently, carbonization, followed by CO₂ activation at 1000 °C was applied to convert the fiber mats into porous carbon nanofibers (CNFs). The addition of 6FDD shows significant effects on the microstructure and enhancement of the surface area of the CNFs. The obtained CNFs show specific surface area as high as 3010 m² g⁻¹ with pore sizes comparable to those of the electrolyte ions (PYR₁₄TFSI). This provides good electrolyte accessibility to the pore of the carbon materials resulting in enhanced energy density compared to the CNFs obtained from pure PBI. Electrodes derived from PBI:6FDD (70 : 30) exhibited outstanding supercapacitor performance in coin cells with a specific capacitance of 142 F g⁻¹ at the scan rate of 10 mV s⁻¹ and energy density of 67.5 W h kg⁻¹ at 1 A g⁻¹ (58 W h kg⁻¹ at 10 A g⁻¹) thus demonstrating promising electrochemical performance for high performance energy storage system.
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    Selectivity of Metal Oxide Atomic Layer Deposition on Hydrogen Terminated and Oxidized Si(001)-(2x1) Surface
    (A V S Amer Inst Physics, 2014-02-10) Longo, Roberto C.; McDonnell, Stephen; Dick, D.; Wallace, Robert M.; Chabal, Yves J.; Owen, James H. G.; Ballard, Josh B.; Randall, John N.; Cho, Kyeongjae; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)
    In this work, the authors used density-functional theory methods and x-ray photoelectron spectroscopy to study the chemical composition and growth rate of HfO₂, Al₂O₃, and TiO₂ thin films grown by in-situ atomic layer deposition on both oxidized and hydrogen-terminated Si(001) surfaces. The growth rate of all films is found to be lower on hydrogen-terminated Si with respect to the oxidized Si surface. However, the degree of selectivity is found to be dependent of the deposition material. TiO₂ is found to be highly selective with depositions on the hydrogen terminated silicon having growth rates up to 180 times lower than those on oxidized Si, while similar depositions of HfO₂ and Al₂O₃ resulted in growth rates more than half that on oxidized silicon. By means of density-functional theory methods, the authors elucidate the origin of the different growth rates obtained for the three different precursors, from both energetic and kinetic points of view.