Guang-Lin Zhao

Nitrogen-Doped Fullerene as a Potential Catalyst for Hydrogen Fuel Cells

We examine the possibility of nitrogen-doped C60 fullerene (N-C60) as a cathode catalyst for hydrogen fuel cells. We use first-principles spin-polarized density functional theory calculations to simulate the electrocatalytic reactions on N-C60. The first-principles results show that an O2 molecule can be adsorbed and partially reduced on the N-C complex sites (Pauling sites) of N-C60 without any activation barrier. Through a direct pathway, the partially reduced O2 can further react with H(+) and additional electrons and complete the water formation reaction (WFR) with no activation energy barrier. In the indirect pathway, reduced O2 reacts with H(+) and additional electrons to form H2O molecules through a transition state (TS) with a small activation barrier (0.22-0.37 eV). From an intermediate state to a TS, H(+) can obtain a kinetic energy of ∼0.95-3.68 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during the WFR. The full catalytic reaction cycles can be completed energetically, and N-C60 fullerene recovers to its original structure for the next catalytic reaction cycle. N-C60 fullerene is a potential cathode catalyst for hydrogen fuel cells.

Ab initio calculations of the electronic structure and optical properties of ferroelectric tetragonal

The electronic structure, charge distribution, effective charge, and charge transfer in ferroelectric tetragonal are carefully studied using a local density functional potential and a self-consistent ab initio LCAO (linear combination of atomic orbitals) method. It is shown that the band gap and low-energy conduction band can be calculated with a reasonable accuracy when the ab initio LCAO method is used with an optimum basis set of atomic orbitals. The calculated optical spectrum, band gap, and effective mass of , obtained from the calculated electronic structure, are in good agreement with experimental results.

Predictions of electronic, structural, and elastic properties of cubic InN

We present theoretical predictions of electronic, structural, and elastic properties of cubic indium nitride in the zine-blende structure (c-InN). Our ab initio, self-consistent calculations employed a local density approximation potential and the Bagayoko, Zhao, and Williams implementation of the linear combination of atomic orbitals. The theoretical equilibrium lattice constant is 5.017A, the band gap is 0.65eV, and the bulk modulus is 145GPa. The band gap is 0.74eV at an experimental lattice constant of 4.98A.

Magnetic graphene oxide nanocomposites: nanoparticles growth mechanism and property analysis

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm−1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10−2 S cm−1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10−2 S cm−1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g−1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively.

Dielectric and microwave attenuation properties of graphene nanoplatelet–epoxy composites

Graphene nanoplatelet (GNP)–epoxy composites were fabricated for the investigation of the dielectric permittivity and microwave absorption in a frequency range from 8 to 20 GHz. The intrinsically conductive GNP particles and polarized interfacial centers in the composites contribute to the microwave absorption. A minimum reflection loss of −14.5 dB at 18.9 GHz is observed for the GNP–epoxy composites with 15 wt. % GNP loading, which is mainly attributed to electric conductivity and the charge multipoles at the polarized interfaces in the GNP–epoxy composites.

Electromagnetic wave absorption of multi-walled carbon nanotube–epoxy composites in the R band

Multi-walled carbon nanotube (MWCNT)–epoxy composites with MWCNT (outer diameter 8–15 nm) loadings from 0.1 to 5 wt% were fabricated. The morphologies, conductivities, dielectric permittivities, and electromagnetic (EM) wave absorptions of the MWCNT–epoxy composites were investigated. The results showed that the EM wave absorptions strongly depended on the complex permittivities of the composites. An abrupt enhancement of conductivity by 9 orders of magnitude for the composite sample with 5 wt% MWCNT loading was observed, which is associated with a sharp improvement in the electromagnetic absorption in the R band (26.5–40 GHz) and is characterized by the formation of a conductive network structure consisting of separated MWCNT aggregates and connected MWCNT bundle bridges in the composites. The electrically-conductive composite allows charge transport between the conductive MWCNT components and contributes to the substantial improvement of the electromagnetic absorption of the MWCNT–epoxy composites.

Enhanced electromagnetic wave shielding effectiveness of Fe doped carbon nanotubes/epoxy composites

Fe doped multi-walled carbon nanotubes (MWCNTs)/epoxy composites were fabricated for the investigation of electromagnetic interference (EMI) shielding. Compared with the pristine MWCNTs, a small amount of Fe doping into the MWCNTs can substantially improve the EMI shielding effectiveness (SE) of MWCNTs/epoxy composites. The highest EMI shielding effectiveness of the composites is −32 to −41 dB in the measured frequency range from 26 to 40 GHz for the sample with 8 wt. % Fe doped MWCNT loading. The contribution of EMI SE of the composites is mainly due to dielectric loss rather than magnetic loss.

Electronic structure and charge transfer in 3C- and 4H-SiC

We utilized a local density functional potential, the linear combination of atomic orbital (LCAO) method, and the BZW procedure to study the electronic structure of 3C- and 4H-SiC. We present the calculated energy bands, band-gaps, effective masses of n-type carriers, and critical point transition energies. There is good agreement between the calculated electronic properties and experimental results. Our preliminary total energy calculations for 3C-SiC found an equilibrium lattice constant of a = 4.35 A, which is in agreement with the experimentally measured value of 4.348 A. The calculated charge transfers indicate that each silicon atom loses about 1.4 electrons that are gained by a carbon atom in both 3C- and 4H-SiC.

Super-small energy gaps of single-walled carbon nanotube strands

The temperature dependence of the resistance measured on long single-walled carbon nanotube (SWNT) strands has been investigated. By applying a simple model to the detailed analysis of our experimental results, we discovered a super-small energy gap of 1–3meV, which is an intrinsic property of the “metallic” SWNT bundles in long SWNT strands.

Morphology and electromagnetic interference shielding effects of SiC coated carbon short fibers

The electromagnetic shielding effectiveness of C–SiC/epoxy composites was investigated and compared with that of carbon fiber/epoxy composites. C–SiCs, short fibers with carbon cores and silicon carbide shells, were fabricated by a carbothermal reduction process using chopped carbon fibers (CFs) and rice husk ash. After presenting the morphology and structure of the C–SiC fibers, the electromagnetic interference shielding effect of SiC coated carbon short fibers is discussed. The Kα-band (26.5–40.0 GHz) shielding studies revealed that the maximum total shielding effectiveness (SET) of the composite with 25 vol% of C–SiCs is 17.07 dB, dominated by absorption, while the composite with 25 vol% of the same sized carbon fibers has a SET of 8.44 dB only.