Papers by Author: Guo Zhong Cao

Abstract: The electrochemical oxidation of sodium borohydride (NaBH4) on Pt electrode in alkaline electrolyte with the addition of thiourea has been studied by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP). NaBH4 is readily to react with hydroxyl groups to release hydrogen through either direct oxidation or catalytic hydrolysis. The experimental results demonstrated that the addition of an appropriate amount of thiourea to the alkaline electrolyte resulted in the suppression of catalytic hydrolysis and diffusion of borohydride ions through the separation membrane.

Abstract: Ammonia borane (AB) with high gravimetric hydrogen capacity is of great interest for storing hydrogen in solid form which is an important issue in the growing field of hydrogen technology. In this work the effects of surface chemistry on dehydrogenation kinetics of carbon cryogel (CC) – ammonia borane nanocomposites have been studied. Boron-modified, nitrogen-modified, and boron-nitrogen- modified CCs were used as scaffold for AB and dehydrogenation kinetics of CC-ABs was studied by means of differential scanning calorimetry (DSC) at multiple heating rates. The results demonstrated that AB incorporated inside the mesopores of CC modified with nitrogen and boron possesses lower activation energy with enhanced kinetics of dehydrogenation due to catalytic effects as compared to AB in unmodified CC under otherwise the same or similar conditions. In addition, the lowest activation energy was observed for boron-modified CC-AB that could be attributed to the destabilization of AB by surface interactions with B2O3 that may accelerate the dehydrogenation process.

Abstract: Hydrogen generated from clean and renewable energy sources has been considered as an alternate fuel to carbon based fossil fuels for several decades. Although many advances in hydrogen production and usage have been made, storing hydrogen remains a significant challenge. Many drawbacks including energy intensive processes, low volumetric densities, and safety concerns are associated with storing hydrogen as pressured or liquefied. Solid state hydrogen storage is considered to be the most promising method as a safe and effective storage option, but there is still no material or method that satisfies the requirements for a practical approach. A feasible hydrogen storage media should address several issues including targeted storage capacities, thermodynamics and hydrogen sorption kinetics, and safety. Nanostructured materials can provide tailor-made properties for storing and releasing hydrogen to fulfill, at least, the partial requirements. This short review, not a comprehensive review of all the materials or technologies in hydrogen storage, summarizes some of the recent developments in application of nanostructures for solid state hydrogen storage; particular attention has been devoted to the most recent development of nanocomposites with tuned dehydrogenation temperatures and kinetics through the control of pore size and surface chemistry.

Abstract: (Ba,Sr)TiO3 thin film has been deposited on Si (001) wafer with the SiO2 layer as the block layer through laser molecular-beam epitaxy using an ultra thin Sr layer as template. X-ray diffraction measurements and the cross-sectional observations under transmission electron microscope indicated that BST was well crystallized. This deposition of Sr layer is considered to remove the thin SiO2 layer to produce a layer, which is crystallized and has a lattice structure matching with that of perovskite BST. The maximum in-plane dielectric tunability is calculated to be 50% at 1 GHz under a moderate DC bias field of 13.3 V/µm. This BST/Si structure is believed to be a promising candidate in the development of ferroelectric BST-based microwave devices.

Abstract: SiO2 films were prepared by atomic layer deposition (ALD) technique, and their physical and electrical properties were characterized for being applied as a gate insulator of low-temperature polysilicon thin-film transistors. ALD SiO2 films were deposited at 350–400 oC using alternating exposures of SiH2Cl2 and O3/O2, and the characteristics of the deposited films were improved with increasing deposition temperature. The ALD films deposited at 400 oC exhibited integrity, surface roughness and leakage current better than those of the conventional plasma-enhanced chemical vapor deposition (PECVD) films.

Abstract: In this seminar, I will present our recent work on the growth and electrochemical properties of single crystalline vanadium pentoxide (V2O5) nanorod and Ni-V2O5·nH2O nanocable arrays. These nanostructures were prepared by solution synthesis and template-based electrodeposition. Processing, morphology, structure and electrochemical properties of these nanostructures will be discussed. These nanostructured electrodes of vanadium pentoxide demonstrate significantly enhanced intercalation capcity and charge/discharge rate compared to the plain film electrodes, due to the high surface area and short diffusion distance offered by nanostructure.

Abstract: This paper introduces a process for the growth of oxide nanorod, nanotube, and nanocable arrays that combines sol preparation and template-based electrophoretic deposition. Examples are shown that the sol electrophoretic deposition is an effective method for the formation of polycrystalline and single crystal oxide nanorod arrays, nanotube arrays and conformal coating of thin films of oxides on metal nanorods to produce metal-oxide core-shell nanocable arrays.