12 Search Results

ABSTRACT In this article, bioplastic polyethylene furanoate (PEF) is synthesized using polycondensation of 2,5‐furandicarboxylic acid and ethylene glycol at a temperature of 220°C using a solid nanowire based super‐acid catalyst. The super acid catalyst is made by phosphating titania nanowires. Specifically, the reactions resulted in over 90% FDCA conversion and 85% PEF yield in a short period of 3 h using superacid catalysts at a loading of < 1% by wt. The mechanical properties of PEF, including glass transition temperature (84°C), melting point (210°C), and crystallinity (1.48 g/cm ³ ), demonstrate the high quality of the PEF produced. Barocaloric properties of resulting PEF polymers are also studied which show promise.

The present development is a metal particle coated nanowire catalyst for use in the hydrodesulfurization of fuels and a process for the production of the catalyst. The catalyst comprises titanium(IV) oxide nanowires wherein the nanowires are produced by exposure of a TiO2—KOH paste to microwave radiation. Metal particles selected from the group consisting of molybdenum, nickel, cobalt, tungsten, or a combination thereof, are impregnated on the metal oxide nanowire surface. The metal impregnated nanowires are sulfided to produce catalytically-active metal particles on the surface of the nanowires The catalysts of the present invention are intended for use in the removal of thiophenic sulfur from liquid fuels through a hydrodesulfurization (HDS) process in a fixed bed reactor. The presence of nanowires improves the HDS activity and reduces the sintering effect, therefore, the sulfur removal efficiency increases.

The development of domestic, environmentally friendly and sustainable sources of energy and liquid fuel is a critical need for the United States (US). Kentucky (KY) is rich in natural energy and agricultural resources that could provide sustainable energy for the state and for the nation. New technology is needed to capture, store, and distribute this sustainable energy in KY. Development of KY’s sustainable energy resources will create economic benefit for the citizens of KY and can serve as a model for other states in the US. Existing technologies for solar energy collection and storage are practical for regions with high and consistent solar intensity, such as the southwest US. Solar energy is plentiful in KY, but is less intense and less regular. As such, novel innovative technology is needed to capture, store, and distribute this energy. KY also has plentiful biomass resources that can be converted to renewable fuels. In addition, the state offers low energy rates, which are conducive for any type of manufacturing industry. A manufacturing R&D center at the University of Louisville (UofL) can help attract high-tech manufacturing industries to the city of Louisville and the state of KY.

All-solid-state batteries that employ superionic solid conductor potentially enable the broadening of battery operation in harsh environments, such as under subzero temperatures and even lower. The solid electrolyte as the key component requires structural stability, high-efficiency of ion transportation channels, and low activation energy to maintain the fast-ionic conduction against temperature drop. Herein, we use 3D superionic conductor Na₃SbS₄ as a model to investigate the structure and conductive mechanism at extremely low temperature. Cryogenic in situ neutron and X-ray diffractions reveal that Na₃SbS₄ maintains a stable tetragonal crystal structure and the anisotropic lattice contraction upon cooling. The dimensions of the S-gate (represented by the S–S pair length) that Na ions hop through in the 3D transportation network is found to maintain open sizes in the xy-plane, contributing to the low activation energy and impressive ionic conductivity. The Na-ion transportation network is demonstrated to be directionally accessible at the extremely low temperature, which reveals the ion conductive mechanism at broadened temperature range in the view of structure. Furthermore, these findings provide valuable guidance in the search for materials as promising solid electrolyte in solid-state batteries to fulfill harsh environmental needs.

Abstract Here, unbiased water splitting with 2% solar‐to‐hydrogen efficiency under AM 1.5 G illumination using new materials based on GaSb _0.03 P _0.97 alloy is reported. Freestanding GaSb _x P _{1− x} is grown using halide vapor phase epitaxy. The native conductivity type of the alloy is modified by silicon doping, resulting in an open‐circuit potential (OCP) of 750 mV, photocurrents of 7 mA cm ⁻² at 10 sun illumination, and corrosion resistance in an aqueous acidic environment. Alloying GaP with Sb at 3 at% improves the absorption of high‐energy photons above 2.68 eV compared to pure GaP material. Electrochemical Impedance Spectroscopy and illuminated OCP measurements show that the conduction band of GaSb _x P _{1− x} is at −0.55 V versus RHE irrespective of the Sb concentration, while photocurrent spectroscopy indicates that only radiation with photon energies greater than 2.68 eV generate mobile and extractable charges, thus suggesting that the higher‐laying conduction bands in the Γ 1 valley of the alloys are responsible for exciton generation.

Undoped hematite nanowire arrays grown using plasma oxidation of iron foils show significant photoactivity ({approx}0.38 mA cm{sup -2} at 1.5 V versus reversible hydrogen electrode in 1 M KOH). In contrast, thermally oxidized nanowire arrays grown on iron exhibit no photoactivity due to the formation of a thick (>7 {micro}m Fe{sub 1-x}O) interfacial layer. An atmospheric plasma oxidation process required only a few minutes to synthesize hematite nanowire arrays with a 1-5 {micro}m interfacial layer of magnetite between the nanowire arrays and the iron substrate. An amorphous oxide surface layer on hematite nanowires, if present, is shown to decrease the resulting photoactivity of as-synthesized, plasma grown nanowire arrays. The photocurrent onset potential is improved after removing the amorphous surface on the nanowires using an acid etch. A two-step method involving high temperature nucleation followed by growth at low temperature is shown to produce a highly dense and uniform coverage of nanowire arrays.

In this study, hydrogen evolution reaction is catalyzed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoO_x/MoS₂ core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ~100 mV improvement in over potential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoO_x core in the core-shell nanowires, which leads to improved electrocatalytic performance.

Significant interest has grown in the development of earth-abundant and efficient catalytic materials for hydrogen generation. Layered transition metal dichalcogenides present opportunities for efficient electrocatalytic systems. Here, we report the modification of 1D MoO_x/MoS₂ core–shell nanostructures by lithium intercalation and the corresponding changes in morphology, structure, and mechanism of H₂ evolution. The 1D nanowires exhibit significant improvement in H₂ evolution properties after lithiation, reducing the hydrogen evolution reaction (HER) onset potential by ~50 mV and increasing the generated current density by ~600%. The high electrochemical activity in the nanowires results from disruption of MoS₂ layers in the outer shell, leading to increased activity and concentration of defect sites. This is in contrast to the typical mechanism of improved catalysis following lithium exfoliation, i.e., crystal phase transformation. As a result, these structural changes are verified by a combination of Raman and X-ray photoelectron spectroscopy (XPS).

Applicability of the Ga(Sb_x)N_1-x alloys for practical realization of photoelectrochemical water splitting is investigated using first-principles density functional theory incorporating the local density approximation and generalized gradient approximation plus the Hubbard U parameter formalism. Our calculations reveal that a relatively small concentration of Sb impurities is sufficient to achieve a significant narrowing of the band gap, enabling absorption of visible light. Theoretical results predict that Ga(Sb_x)N_1-x alloys with 2-eV band gaps straddle the potential window at moderate to low pH values, thus indicating that dilute Ga(Sb_x)N_1-x alloys could be potential candidates for splitting water under visible light irradiation.

The Kentucky EPSCoR Program supported an inter-university, multidisciplinary energy-related research cluster studying nanomaterials for converting solar radiation and residual thermal energy to electrical energy and hydrogen. It created a collaborative center of excellence based on research expertise in nanomaterials, architectures, and their synthesis. The project strengthened and improved the collaboration between the University of Louisville, the University of Kentucky, and NREL. The cluster hired a new faculty member for ultra-fast transient spectroscopy, and enabled the mentoring of one research scientist, two postdoctoral scholars and ten graduate students. Work was accomplished with three focused cluster projects: organic and photoelectrochemical solar cells, solar fuels, and thermionic energy conversion.