Chun-Sheng Liu

Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters

Multi-walled carbon nanotubes (MWNTs) with different mean outer diameters in the range of 13-53 nm, synthesized by the catalytic decomposition of hydrocarbons using a floating catalyst method, were purified and pretreated with the same procedure for volumetric hydrogen adsorption/desorption measurements. It was found that the hydrogen storage capacity of the purified and pretreated MWNTs was proportional to their diameter, and that hydrogen in all types of MWNTs measured could not be completely desorbed at room temperature and ambient pressure. A possible mechanism for the above behavior was proposed based on the results of cryogenic nitrogen adsorption analysis and high-resolution transmission electron microscopy observations. It was considered that small carbon islands might be the main hydrogen adsorption site in MWNTs. The effects of metal catalyst as well as an etched cavity on the surface of MWNTs on the hydrogen adsorption/desorption of MWNTs were also discussed

Boron-tuned bonding mechanism of Li-graphene complex for reversible hydrogen storage

Based on first-principles density functional theory, we show that boron-doping significantly enhances the Li bond strength on the graphene. The transition from s–p hybridization of the Li-graphene complex to p–p hybridization of the Li-coated boron-doped graphene is responsible for the enhanced binding energy. The charge redistribution induced by boron-doping gives rise to two parts of an electrostatic potential energy (one is around the Li atom and the other is parallel to the graphene plane). Four polarized H2 molecules are attached to one Li atom with an optimal binding energy of ∼0.13u2002eV/H2.

Volumetric hydrogen storage in single-walled carbon nanotubes

Macroscopically long ropes of aligned single-walled carbon nanotubes (SWNTs), synthesized by a hydrogen and argon arc discharge method, were cold pressed into tablets without any binder for measurements of their volumetric hydrogen storage capacity. The typical apparent density of the tablets was measured to be around 1.7 g/cm(3) with respect to a molding pressure of 0.75 Gpa. A volumetric and mass hydrogen storage capacity of 68 kg H-2/m(3) and 4.0 wt %, respectively, was achieved at room temperature under a pressure of 11 MPa for suitably pretreated SWNT tablets, and more than 70% of the hydrogen adsorbed can be released under ambient pressure at room temperature. Pore structure analysis indicated that the molding process diminished the mesopore volume of the SWNT ropes, but exerts little influence on their intrinsic pore textures

Li-doped B2C graphene as potential hydrogen storage medium

Based on first-principles density functional theory, we show that Li-doped B2C graphene can serve as a high-capacity hydrogen storage medium with the gravimetric density of 7.54 wtu2009%. The present results indicate that the strong binding of Li onto the substrate comes from the hybridizations of Bu20022p and Cu20022p orbitals with the partial occupancy of Liu20022p orbitals. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of H2 molecules and the resulting adsorption energy is in the range of 0.12–0.22u2002eV/H2. The system reported here is favorable for the reversible hydrogen adsorption/desorption at the room temperature.

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

Non-hexagonal symmetry-induced functional T graphene for the detection of carbon monoxide

Unlike on hexagonal graphene where Li atoms tend to cluster, using density functional theory, we demonstrate that Li atoms remain isolated on tetrasymmetrical T graphene due to a nonuniform charge distribution in T graphene. Furthermore, we examine the adsorption of several common gas molecules and find that Li-decorated T graphene exhibits a high sensitivity to CO. The CO adsorption strength can be manipulated by an external electric field, resulting in a short recovery time. Our results provide an insight to build promising nanosensors based on two-dimensional carbonic materials beyond hexagonal symmetry.

Titanium-capped carbon chains as promising new hydrogen storage media

The capacity of Ti-capped sp carbon atomic chains for use as hydrogen storage media is studied using first-principles density functional theory. The Ti atom is strongly attached at one end of the carbon chains via d-p hybridization, forming stable TiC(n) complexes. We demonstrate that the number of adsorbed H(2) molecules on Ti through Kubas interactions depends upon the chain types. For polyyne (n even) or cumulene (n odd) structures, each Ti atom can hold up to five or six H(2) molecules, respectively. Furthermore, the TiC(5) chain effectively terminated on a C(20) fullerene can store hydrogen with an optimal binding energy of 0.52 eV per H(2) molecule. Our results reveal a possible way to explore high-capacity hydrogen storage materials in truly one-dimensional carbon structures.

Fabrication and characterization of heteroepitaxial bilayers of La-Ca-Mn-O/Y-Ba-Cu-O

We have fabricated La0.67Ca0.33MnO3/YBa2Cu3Oy heteroepitaxial bilayers on SrTiO3 (1 0 0) substrates by rf magnetron sputtering. The La0.67Ca0.33MnO3/YBa2Cu3Oy bilayers were characterized by X-ray diffraction, rocking curve measurements, scanning electron microscope and dc four-probe measurements. Both La0.67Ca0.33MnO3 and YBa2Cu3Oy layers show excellent crystallinity indicated. by their sharp and narrow rocking curves. The La0.67Ca0.33MnO3/YBa2Cu3Oy bildyers exhibit a very smooth surface. The relation between the superconducting critical current density of YBa(2)Cu(3)O(y)and temperature was alsoinvestigated

Magnetic nanocables—Silicon carbide sheathed with iron-oxide-doped amorphous silica

High-purity nanocables of iron-containing amorphous-silica-sheathed silicon carbide were synthesized by a thermal reaction method using silicon wafer as the silicon source and growth substrate, and ferrocene as the carbon and iron catalyst precursor. The nanocables were tens of mu m in length and 40-60 nm in diameter. Iron oxide nanoparticles with a mean diameter of 5 nm were dispersed evenly in the amorphous silica layer. The nanocables were found to be ferromagnetic at both 10 K and room temperature, which indicates that they may have important potential applications in electromagnetic nanodevices.

Excellent buffer layer for growing high-quality Y-Ba-Cu-O thin films

Eu2CuO4 (ECO) has been used as a buffer layer for growing of YBa2Cu3O7-delta (YBCO) thin films on SrTiO3(100) and Y-stabilized ZrO2(100) substrates. The epitaxy, crystallinity, and surface of YBCO thin films have been significantly improved by using ECO buffer layer as investigated by x-ray diffraction, rocking curves, scanning electron microscope, surface step profiler, and x-ray small-angle reflection. The best value of the full width at half-maximum of the YBCO(005) peak can be greatly reduced down to less than 0.1 degrees. The scanning-electron-microscope photos indicate a very smooth surface for the YBCO thin films. The average roughness is less than 5 nm over a wide scanning region of 2000 mum. The results of x-ray small-angle reflection indicate a very clear and flat interface between YBCO and ECO layers. Meanwhile, the resistivity of ECO is about 20 times higher than that of PrBa2Cu3Oy at the boiling point of liquid nitrogen. Our results suggest that ECO should be a good barrier candidate for fabricating high-T-c, superconductor junctions.