Pengfei Yuan

Li and Ca Co-decorated carbon nitride nanostructures as high-capacity hydrogen storage media

Using first-principles method based on density functional theory, we perform a detailed study of the hydrogen storage properties of Li and Ca co-decorated graphene-like carbon nitride (g-CN) nanostructures. The results show that the average adsorption energy of the molecular hydrogen is ∼0.26 eV/H2, which is acceptable for reversible H2 adsorption/desorption near ambient temperature. Moreover, the findings also show that the storage capacity of the Li and Ca co-decorated g-CN can reach up to 9.17 wt %, presenting a good potential as hydrogen storage material. Regarding the H2 adsorption mechanism, it is demonstrated that the Li adatoms become positively charged through charge transferring to g-CN and then bind hydrogen molecules via the polarization mechanism.

Au nanoparticle decorated N-containing polymer spheres: additive-free synthesis and remarkable catalytic behavior for reduction of 4-nitrophenol

We demonstrated a simple, one-step route for assembling Au nanoparticles (NPs) on N-containing polymer nanospheres through in situ reductive growth process.Using resorcinol–melamine–formaldehyde resin nanospheres (RMF NSs) as a functional platform, neither a surfactant/ligand nor pretreatment is needed in the synthetic process of Au@RMF NSs hybrid nanostructure. When used as a catalytic media for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol, the Au@RMF NSs hybrid nanostructures show significantly enhanced catalytic performance than the ever reported Au-based catalyst. The absorption modal of 4-NP on this nanostructure is also discussed by theoretical calculations using density functional theory. The calculated results verify the preferential capture of 4-NP by the N-containing functionalities of RMF NSs, which is critical step for the acceleration of Au-based catalytic reaction kinetics, leading to the remarkable improved catalytic behavior. The superior features of RMF NSs as well as minimal economical cost compared with other polymer and non-polymer will promote further interest in the field of N-containing catalysis.

Carbon Nanosheets Containing Discrete Co-Nx-By-C Active Sites for Efficient Oxygen Electrocatalysis and Rechargeable Zn–Air Batteries

Structural and compositional engineering of atomic-scaled metal-N-C catalysts is important yet challenging in boosting their performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here, boron (B)-doped Co-N-C active sites confined in hierarchical porous carbon sheets (denoted as Co-N,B-CSs) were obtained by a soft template self-assembly pyrolysis method. Significantly, the introduced B element gives an electron-deficient site that can activate the electron transfer around the Co-N-C sites, strengthen the interaction with oxygenated species, and thus accelerate reaction kinetics in the 4e- processed ORR and OER. As a result, the catalyst showed Pt-like ORR performance with a half-wave potential (E1/2) of 0.83 V versus (vs) RHE, a limiting current density of about 5.66 mA cm-2, and higher durability (almost no decay after 5000 cycles) than Pt/C catalysts. Moreover, a rechargeable Zn-air battery device comprising this Co-N,B-CSs catalyst shows superior performance with an open-circuit potential of ∼1.4 V, a peak power density of ∼100.4 mW cm-2, as well as excellent durability (128 cycles for 14 h of operation). DFT calculations further demonstrated that the coupling of Co-Nx active sites with B atoms prefers to adsorb an O2 molecule in side-on mode and accelerates ORR kinetics.

Electronic and optical properties of quaternary alloy GaAsBiN lattice-matched to GaAs

Employing first-principles combined with hybrid functional calculations, the electronic and optical properties of GaAs alloyed with isovalent impurities Bi and N are investigated. As GaAsBiN alloy is a quaternary alloy, the band gap and the lattice constant of the alloy can be individually tuned. Both impurities are important to the valence band and conduction band of the alloy, with the band gap of the alloy being dramatically reduced by Bi 6p states and N localized 2s states. Interestingly, the calculated optical properties of the quaternary alloy are similar to those of undoped GaAs except that the absorption edge has a redshift toward lower energy. These results suggest potential interest in the long-wavelength applications of GaAsBiN alloy.

Atomistic view of thin Ni/Ni3Al (0 0 1) under uniaxial tension of twist grain boundaries

Atomic motion and the structure response of grain boundaries (GBs) are essential to the plastic deformation of small-volume polycrystal systems, especially for thin materials that exhibit some dramatic characteristics. Here, the microstructure and properties of thin Ni/Ni3Al (0 0 1) with the uniaxial tension of twist GBs are investigated using molecular dynamics (MD) simulations with an embedded atom (EAM) potential. We find that low angle twist GB dislocations propagate mainly from the corners to the center of the interface, and for high angle twist GBs they originate from the edge of the interface but do not extend to the center. In the process of plastic deformation, both low angle and high angle twist GB fractures occur in the center of the interface, which is completely different from the situation of thick materials reported by other references. More interestingly, the fracture patterns between low angle and high angle twist GBs exhibit extremely different performance due to the different characteristics of the initial dislocation structures in the interfaces.

STRUCTURAL AND ELECTRONIC PROPERTIES OF ZINCBLENDE AlInN ALLOY: A HYBRID DENSITY FUNCTIONAL STUDY

Conventional local and semilocal density functionals cannot predict correct bandgap energy for semiconductors especially the indium compounds. By employing the density functional theory calculations with a hybrid functional, we studied the bandgap energy and structure properties of AlN and InN compounds as well as their ternary AlInN alloys. We showed that by adjusting the screening parameter in the hybrid functional, the bandgaps calculated are in good agreement with the experimental data. A 2.54 eV natural valence band offset between AlN and InN is found with the hybrid density functional study. Furthermore, we studied the bandgap and band bowing parameter for AlInN alloys by using the hybrid density functional. The bandgap and band bowing parameters obtained are consistent with experimental and other theoretical results. Our results revealed that, although the PBE functional underestimates the bandgap energy for binary compound and ternary AlInN alloy, their band bowing parameters are still reasonable and valid. Our results should be useful for experiment and optoelectronic device applications.

ATOMISTIC VIEWS OF DYNAMICAL FRACTURE INSTABILITIES IN SILICON: MOLECULAR DYNAMICS STUDIES

This study investigates the crystallographic orientations most widely known to exhibit fractures in silicon, such as those on the (111) plane cracks travelling along the

Electronic properties of anatase TiO2 doped by lanthanides: A DFT+U study

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Negative thermal expansion correlated with polyhedral movements and distortions in orthorhombic Y2Mo3O12

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Theoretical study of negative thermal expansion mechanism of ZnF2

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