Placidus B. Amama

Magnetic field-induced fabrication of Fe3O4/graphene nanocomposites for enhanced electrode performance in lithium-ion batteries

We report a novel magnetic field-induced approach for the fabrication of nanoporous and wrinkled Fe3O4/reduced graphene oxide (RGO) anode materials for lithium ion batteries (LIBs). The applied magnetic field improves the interfacial contact between the anode and current collector and increases the stacking density of active material. This facilitates the kinetics of Li ions and electrons, electrode durability, and surface area of active material. As a result, at relatively low specific currents (157 mA g−1), wrinkled Fe3O4/RGO anodes show high reversible specific capacities (up to 903 mA h g−1 at 157 mA g−1). At high discharge rate (1.57 A g−1), the specific capacity of wrinkled anodes stay at 345 mA h g−1 (with capacity retention of 90%) after 100 discharge/charge cycles compared to the rapid capacity fading associated with smooth or unwrinkled anodes with a specific capacity of 178 mA h g−1 after the same number of cycles. These results demonstrate the benefit of strong magnetic field treatment during fabrication of nanocomposites containing magnetic nanoparticles.

Microgel-assisted assembly of hierarchical porous reduced graphene oxide for high-performance lithium-ion battery anodes

Graphene has emerged as one of the foremost candidates for replacing graphite anodes in lithium-ion batteries (LIBs) due to its unique physical and electrochemical properties. Most techniques for synthesis of graphene-based electrode materials utilize graphene oxide (GO). However, restacking of GO sheets during common fabrication processes usually results in significant loss of usable Li-insertion sites, and consequently, a substantial decrease in cycling performance of the electrode. In this work, we demonstrate a facile and scalable approach for fabrication of 3D, hierarchical macro/mesoporous reduced graphene oxide (RGO) anodes for LIBs using a polymer sphere (PS) microgel as a template. The synthesis process involves controlled encapsulation of GO sheets on the surface of thermal degradable PS microgels, followed by shrinkage of PS microgels to generate GO wrinkles. The GO-wrapped cross-linked PS swells to a microgel in N-methyl-2-pyrrolidone (NMP), while it shrinks after replacing the NMP with distilled water. The overall specific surface area of the resulting porous/wrinkled RGO with mesopores and macropores, obtained by annealing the wrinkled GO@shrunk PS, increases from 96 m2 g−1 to 276 m2 g−1; the highly porous structure also shortens the transport length of Li ions. The porous/wrinkled RGO anode material achieves a high reversible capacity and durability (∼720 mA h g−1 at 0.2C after 200 cycles), and a high rate capability (∼160 mA h g−1 at 20C). The electrode performance is comparable to the best RGO anodes. The microgel-assisted method opens up a promising route for potentially controlling the properties of 3D graphene-based electrodes.

Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes

Growth of high quality, dense carbon nanotube (CNT) arrays via catalytic chemical vapor deposition (CCVD) has been largely limited to catalysts supported on amorphous alumina or silica. To overcome the challenge of conducting CNT growth from catalysts supported on conductive substrates, we explored a two-step surface modification that involves ion beam bombardment to create surface porosity and deposition of a thin AlxOy barrier layer to make the surface basic. To test the efficacy of our approach on a non-oxide support, we focus on modification of 316 stainless steel (SS), a well-known inactive substrate for CNT growth. Our study reveals that ion beam bombardment of SS has the ability to reduce film thickness of the AlxOy barrier layer required to grow CNTs from Fe catalysts to

Understanding properties of engineered catalyst supports using contact angle measurements and X-Ray reflectivity

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Study of mesoporous catalysts for conversion of 2,3-butanediol to butenes

~ 5 nm, which is within the threshold for the substrate to remain conductive. Additionally, catalysts supported on ion beam-damaged SS with the same AlxOy thickness show improved particle formation, catalyst stability, and CNT growth efficiency, as well as producing CNTs with higher quality and density. Under optimal reaction conditions, this modification approach can lead to CNT growth on other nontraditional substrates and potentially benefit applications that require CNTs be grown on a conductive substrate.