Platinum Single Atoms Supported on Nanoarray-Structured Nitrogen-Doped Graphite Foil with Enhanced Catalytic Performance for Hydrogen Evolution Reaction.

Platinum-based single-atom catalysts (SACs) are among the most promising candidates for the practical applications of electrochemical hydrogen evolution reaction (HER), but their catalytic efficiency remains to be further enhanced. Herein, a well-designed nanoarray-structured nitrogen-doped graphite foil (NNGF) substrate is introduced to support Pt SACs in Pt-N4 construction (Pt1/NNGF) for HER. Within NNGF, the constructed nanoarray-structured surficial layer for supporting Pt SACs could enhance the exposure of active sites to the electrolyte and improve the reaction and diffusion kinetics; meanwhile, the retained graphite structures in bulk NNGF provide not only the required electrical conductivity but also the mechanical stability and flexibility. Because of such double-layer structures of NNGF, stable Pt-N4 construction, and binder-free advantages, the Pt1/NNGF electrode exhibits a low overpotential of 0.023 V at 10 mA cm-2 and a small Tafel slope of 29.1 mV dec-1 as well as an excellent long-term durability.

Activation and Disproportionation of Zr2Fe Alloy as Hydrogen Storage Material.

As a hydrogen storage material, Zr2Fe alloy has many advantages such as fast hydrogen absorption speed, high tritium recovery efficiency, strong anti-pulverization ability, and difficulty self-igniting in air. Zr2Fe alloy has lower hydrogen absorption pressure at room temperature than LaNi5 alloy. Compared with the ZrVFe alloy, the hydrogen release temperature of Zr2Fe is lower so that the material can recover hydrogen isotopes at lower hydrogen concentration efficiently. Unfortunately, the main problem of Zr2Fe alloy in application is that a disproportionation reaction is easy to occur after hydrogen absorption at high temperature. At present, there is little research on the generation and influencing factors of a disproportionation reaction in Zr2Fe alloy. In this paper, the effects of temperature and hydrogen pressure on the disproportionation of Zr2Fe alloy were studied systematically. The specific activation conditions and experimental parameters for reducing alloy disproportionation are given, which provide a reference for the specific application of Zr2Fe alloy.

Electric Properties of Molecule Zr2Fe Based on the Full Relativistic Theory.

The present work is devoted to the study of the electric properties: electric dipole moment, electric quadrupole moment, electric field gradients and electric dipole polarizability of molecule Zr2Fe on base of the full relativistic theory with basis set 3⁻21G. The electric dipole moment of Zr2Fe is symmetrical to the axis of C 2 V -the vector sum of two projections for two chemical bond FeZr (3.2883 Å), based on when there is charge distribution. The force constant k 2 is directly connected with electric field gradients.

Structures, spectroscopic and thermodynamic properties of U2On (n = 0 ∼ 2, 4) molecules: a density functional theory study.

The equilibrium structures, spectroscopic and thermodynamic parameters [entropy (S), internal energy (E), heat capacity (C p)] of U2, U2O, U2O2 and U2O4 uranium oxide molecules were investigated systematically using density functional theory (DFT). Our computations indicated that the ground electronic state of U2 is the septet state and the equilibrium bond length is 2.194 Å; the ground electronic state of U2O and U2O2 were found to be X³Φ and X³Σ(g) with stable C(∞v) and D(∞h) linear structures, respectively. The bridge-bonded structure with D(2h) symmetry and X³B1(g) state is the most stable configuration for the U2O4 molecule. Mulliken population analyses show that U atoms always lose electrons to become the donor and O atoms always obtain electrons as the acceptor. Molecular orbital analyses demonstrated that the frontier orbitals of the title molecules were contributed mostly by 5f atomic orbitals of U atoms. Vibrational frequencies analyses indicate that the maximum absorption peaks stem from the stretching mode of U-O bonds in U2O, U2O2 and U2O4. In addition, thermodynamic data of U2O(n) (n = 0 ∼ 4) molecules at elevated temperatures of 293.0 K to 393.0 K was predicted.

Geometrical and electronic structures of small W(n) (n = 2-16) clusters.

The geometrical and electronic structures of W(n) (n=2-16) clusters are investigated within the framework of a gradient-corrected density functional theory. The close-packed configurations are preferred for small tungsten clusters up to n=16. The most energetic favorable structures of W(14), W(15), and W(16) clusters, exhibiting similar electronic band structures, are all formed based on body centered cubic (bcc) unit. The clusters with size of n=8, 12, and 15 are found to be more stable with respect to their respective neighbors. The analyses of atomic orbit projected density of states and highest occupied molecular orbital, lowest unoccupied molecular orbital isosurfaces indicate that 5d electrons play a dominant role in the chemical activities of tungsten clusters. The clearly s-d hybridizations are primary presented in bonding W atoms of smaller clusters, as the cluster sizes increase, the 6p orbitals are gradually involved in chemical bonding. Our calculated vertical ionization potentials (VIPs) indicate that the W(8) and W(12) clusters correspond to the high VIPs. The vertical electron affinities are slightly underestimated in our investigation, but follow the trends of experimental data in principle.